Rechner Startet Nicht Bei Zwei Monitoren An Displayport

Diagnose why your computer won’t start with two monitors connected via DisplayPort

Comprehensive Guide: Computer Won’t Start with Two Monitors on DisplayPort

When your computer fails to start properly with two monitors connected via DisplayPort, it’s typically related to one of several technical issues involving bandwidth limitations, driver conflicts, or hardware compatibility. This comprehensive guide will walk you through the most common causes and solutions for this frustrating problem.

Understanding the DisplayPort Multi-Monitor Architecture

DisplayPort uses a fundamentally different architecture than HDMI or DVI when it comes to multi-monitor setups. The key concepts you need to understand are:

1. Single-Stream Transport (SST): Traditional one-to-one connection where each DisplayPort output drives one monitor
2. Multi-Stream Transport (MST): Allows daisy-chaining multiple monitors from a single DisplayPort output (requires MST-compatible monitors)
3. Bandwidth Allocation: DisplayPort 1.2 provides 17.28 Gbps, 1.4 provides 25.92 Gbps, and 2.0 provides 77.37 Gbps of total bandwidth
4. DPCD (DisplayPort Configuration Data): The communication protocol between source and sink devices

Top 7 Reasons Your PC Won’t Start with Dual DisplayPort Monitors

Issue	Likelihood	Difficulty to Fix	Common Symptoms
Insufficient GPU bandwidth	High	Medium	Black screens, no POST, or single monitor only
Outdated GPU drivers	Very High	Easy	Flickering, incorrect resolutions, no signal
Faulty DisplayPort cables	High	Easy	Intermittent connection, no signal on one monitor
BIOS/UEFI settings	Medium	Medium	No video output at all, or only integrated graphics works
Monitor EDID issues	Medium	Hard	Incorrect resolutions, color issues, no signal
Power delivery problems	Low	Medium	System powers on but no display, random reboots
Windows display settings	Medium	Easy	Monitors detected but not displaying, wrong order

Step-by-Step Troubleshooting Guide

1. Verify Basic Connections

• Ensure both monitors are powered on and set to the correct input source
• Try different DisplayPort cables (preferably certified ones)
• Test each monitor individually to confirm they work
• Check for physical damage to ports on both GPU and monitors

2. Check GPU Bandwidth Limitations

Modern GPUs have finite display output bandwidth. The table below shows common GPU display output capabilities:

GPU Model	Max DisplayPort 1.4 Outputs	Max Resolution @60Hz	Max Resolution @144Hz	MST Support
NVIDIA RTX 4090	4	4× 4K	2× 4K or 4× 1440p	Yes
AMD RX 7900 XTX	4	4× 4K	2× 4K or 4× 1440p	Yes
Intel Arc A770	4	4× 4K	2× 4K or 3× 1440p	Yes
NVIDIA GTX 1650	3	3× 4K	1× 4K or 2× 1440p	Limited
Integrated Graphics (Intel UHD)	3	2× 4K	1× 4K or 2× 1080p	Basic

If your combination exceeds these limits, you’ll need to:

• Lower refresh rates
• Reduce resolutions
• Use a different connection type for one monitor (HDMI)
• Add a second GPU (for workstations)

3. Update Graphics Drivers

1. Boot into Safe Mode if necessary (hold Shift while clicking Restart in Windows)
2. Uninstall current GPU drivers using Display Driver Uninstaller (DDU)
3. Download latest drivers from:
   • NVIDIA
   • AMD
   • Intel
4. Install drivers in Clean Install mode
5. Reboot and test with one monitor first, then add the second

4. Adjust BIOS/UEFI Settings

Critical settings to check:

• Primary Display Adapter: Set to PCIe/PEG (not iGPU)
• Above 4G Decoding: Enable (for modern GPUs)
• Resizable BAR: Enable (if available)
• CSM (Compatibility Support Module): Disable (use UEFI only)
• Multi-Monitor Support: Enable if available

5. Test with Different Configurations

Systematically test different setups to isolate the issue:

1. Single monitor via DisplayPort – does it work?
2. Single monitor via HDMI – does it work?
3. Two monitors with one on DisplayPort and one on HDMI – does it work?
4. Two monitors with both on HDMI (if possible) – does it work?
5. Different DisplayPort versions (try 1.2 vs 1.4 cables)

Advanced Solutions for Persistent Issues

DisplayPort Multi-Stream Transport (MST) Troubleshooting

If you’re using MST (daisy-chaining or hubs):

• Verify all monitors in the chain support MST (check specifications)
• Ensure the first monitor in the chain is connected directly to the GPU
• Try a different MST hub if using one
• Check for MST firmware updates for your monitors
• In Windows, open dxdiag and check the “Display” tab for MST information

EDID Emulation and Custom Resolutions

Extended Display Identification Data (EDID) issues can prevent monitors from being recognized:

1. Use a tool like Monitor Asset Manager to read EDID
2. For NVIDIA GPUs, use the Custom Resolution tool in NVIDIA Control Panel
3. For AMD GPUs, use Radeon Software to create custom profiles
4. Consider an EDID emulator device if monitors have corrupt EDID

Power Management Workarounds

Some systems have issues with DisplayPort when power saving features are enabled:

• Disable “DisplayPort Deep Color” in GPU control panel
• Set PCIe Link State Power Management to “Off” in Windows Power Options
• Disable “Ultra Low Power State” in AMD Radeon Settings
• Try setting Windows power plan to “High Performance”

Preventing Future DisplayPort Issues

To maintain stable multi-monitor operation:

• Always use high-quality, certified DisplayPort cables
• Keep GPU drivers updated (but don’t install every beta version)
• Update monitor firmware when available
• Avoid mixing different DisplayPort versions in a daisy-chain
• Use a UPS to prevent power-related corruption
• Document your working configuration for quick recovery

Authoritative Resources:

Official DisplayPort Standard Organization

VESA (Video Electronics Standards Association)

NVIDIA Multi-Monitor Technology Whitepaper

NVIDIA Corporation

AMD Eyefinity Multi-Display Technology

Advanced Micro Devices, Inc.

Frequently Asked Questions

Why does my computer work with one DisplayPort monitor but not two?

This typically indicates a bandwidth limitation. When you connect a second monitor, the total bandwidth requirement exceeds what your GPU’s DisplayPort controller can provide. Modern GPUs have multiple display controllers, but each has finite bandwidth (especially with high refresh rates or resolutions).

Can I mix DisplayPort versions in a daisy-chain?

While technically possible, it’s not recommended. The chain will operate at the lowest common version’s specifications. For example, if you have a DisplayPort 1.4 GPU connected to a 1.2 monitor which then connects to a 1.4 monitor, the entire chain will operate at 1.2 specifications, potentially causing compatibility issues.

Why does my second monitor work after Windows loads but not during POST?

This suggests the issue is with your motherboard’s UEFI/BIOS DisplayPort implementation. Many motherboards only fully initialize all display outputs after the operating system takes control. Solutions include:

• Updating your motherboard BIOS
• Enabling “Above 4G Decoding” in BIOS
• Using a different GPU slot if available
• Adding a delay in BIOS for display initialization

How can I check if my DisplayPort cable is the problem?

DisplayPort cables are particularly susceptible to issues because they carry both video and auxiliary data. To test:

1. Try a known-good cable (preferably certified)
2. Check for physical damage to connectors
3. Test the cable with different monitors
4. Look for the DisplayPort certification logo on the cable
5. Try gently wiggling the cable while the system is on to check for intermittent connections

What’s the difference between active and passive DisplayPort adapters?

This is crucial for multi-monitor setups:

• Passive adapters: Simply rewire the signals (e.g., DisplayPort to HDMI). Only work when the source can natively output the target signal type.
• Active adapters: Contain electronics to convert between signal types. Required when the source cannot natively output the target signal (e.g., DisplayPort to dual-link DVI).

For dual-monitor setups, active adapters are generally more reliable but more expensive.