So your monitor says No Signal and you're staring at a black screen while the PC fans spin like nothing's wrong. Annoying, right? The good news: in most cases this isn't a dead monitor or a fried GPU. It's a connection or handshake problem. Here are the three causes that actually matter, in the order you should check them.
1. Loose cable or wrong input selected (90% of cases)
What's actually happening here is the monitor is powered on and scanning for a signal, but it's either looking at the wrong port or the cable isn't making solid contact. This is by far the most common cause. HDMI and DisplayPort cables don't click into place like they claim they do. A 1mm pull-out is enough to drop the signal.
Real-world trigger: you moved the desk to vacuum, or the cat brushed the back of the tower. Suddenly, no signal.
Fix it in this order:
- Reseat both ends of the cable. Unplug it fully from the monitor and the GPU, then push it back in until you feel or hear it click. DisplayPort has a little latch tab — press it fully.
- Press the monitor's input/source button. Cycle through HDMI 1, HDMI 2, DisplayPort, USB-C, whatever's listed. Stop on the one that matches your cable. Don't assume Auto works — Auto often times out before the GPU's output negotiates.
- Check you're plugged into the GPU, not the motherboard. If you have a discrete GPU (a card in a PCIe slot) and you plugged the monitor into the motherboard's HDMI port, you'll get no signal unless your CPU has integrated graphics enabled. This trips up a ton of people after a rebuild.
Skip the $30 HDMI cable from the gas station. Cheap cables with thin conductors fail at 4K/120Hz or long runs. A $12 Amazon Basics 2.1 cable is fine, but if you're running 3440x1440 at 144Hz, buy a VESA-certified DisplayPort 1.4 cable.
2. GPU output or driver issue
If reseating and switching inputs didn't help, the problem is upstream — the GPU isn't actually sending a signal. This usually shows up right after a Windows update, a GPU driver update, or a fresh build.
What's happening: the GPU either isn't detecting the display, is outputting to a different port than you expect, or the driver crashed and hasn't recovered.
Try these in order:
- Test a different port on the GPU. GPUs have 3-4 outputs and one of them can fail. If HDMI works but DisplayPort doesn't, you've narrowed it down.
- Boot into Safe Mode. Hold
Shiftwhile clicking Restart, then navigate to Troubleshoot → Advanced → Startup Settings → Safe Mode. If you get a picture in Safe Mode, it's a driver problem, not hardware. - Reinstall the GPU driver with DDU. Display Driver Uninstaller wipes every trace of the old driver — the real fix when Windows Update installs a broken driver behind your back.
Open an admin Command Prompt and run:
pnputil /enum-devices /class DisplayThat lists every display adapter Windows sees. If your GPU isn't in the list, the card isn't being detected at all — reseat the GPU in its PCIe slot and check the power cables (the 8-pin or 12VHPWR connectors need to be fully clicked in).
3. EDID handshake failure
This one's sneaky. Your GPU and monitor do a little digital handshake where the monitor sends its EDID (Extended Display Identification Data) — a tiny data block describing its native resolution, refresh rate, and supported modes. When that handshake fails, the GPU has no idea what it's driving and outputs nothing. Result: No Signal, even though everything's plugged in correctly.
Triggers I've seen: a KVM switch in the chain, a DisplayPort MST hub, a monitor that wakes from sleep before the GPU, or a bad DisplayPort cable where pin 20 is wired when it shouldn't be. That last one is a real thing — cheap DP cables sometimes wire pin 20 (the 3.3V power pin) to both ends, which creates a loop and confuses the handshake. VESA-certified cables leave pin 20 unconnected.
Fixes:
- Unplug the monitor's power for 60 seconds. This clears the EDID cache in the monitor's controller. Plug it back in and power on the PC first, then the monitor.
- Check the cable's pin 20. If you have a multimeter, test continuity between pin 20 on both ends. If it beeps, the cable is defective. Throw it away.
- Bypass the KVM or hub. Connect the monitor directly to the GPU to isolate the problem.
- Force a specific mode. In Windows, right-click the desktop → Display settings → Advanced display → choose a lower refresh rate. If 144Hz fails but 60Hz works, the cable or monitor firmware is the bottleneck.
Quick reference: which fix do I try first?
| Symptom | Most likely cause | First thing to try |
|---|---|---|
| No Signal after moving the PC | Loose cable | Reseat both cable ends and press monitor Input |
| No Signal right after Windows/driver update | GPU driver crash | Boot into Safe Mode, then run DDU and reinstall driver |
| No Signal only after sleep/wake | EDID handshake | Unplug monitor power for 60s, power PC first |
| No Signal with a KVM or hub in the chain | EDID over MST/KVM | Bypass the KVM and connect directly |
| One port works, another doesn't | Dead GPU port | Use the working port; RMA the card if under warranty |
| No Signal on a brand-new build | Monitor plugged into motherboard | Move the cable to the GPU's output |
One last thing — if you've tried all three and still get No Signal, test the monitor on a laptop or another PC. If it works there, the problem is your GPU or motherboard. If it doesn't, the monitor's input board is dead and it's time for a repair or replacement.