You hit the power button, the fans spin up, the RGB lights do their little dance, and the monitor just sits there blinking "No Signal" at you. Had a client last month, a two-person accounting shop, call me in a panic because their main workstation wouldn't display anything the morning before a filing deadline. Turns out the DisplayPort cable had worked itself loose when someone nudged the desk. Five seconds of reseating the plug. Two hours of their morning saved.
This error shows up most when you've just moved the machine, cleaned behind the desk, swapped a GPU, or added a second monitor. Sometimes it appears out of nowhere after a Windows update or a driver bump. The monitor isn't broken, and your computer probably isn't either. Something between the GPU and the panel isn't talking.
What "No Signal" Actually Means
The monitor is awake and scanning its inputs. It's getting power, the backlight is on, the on-screen menu works. What it isn't getting is a valid video signal on whichever input it's set to. That's the whole message. It doesn't mean the GPU is dead, and it doesn't mean Windows failed to boot. It means the handshake between the graphics card and the display didn't happen.
That handshake has three parts: the cable, the port on the GPU, and the port on the monitor. Any one of them failing gives you the same blank stare. Also in the mix is the monitor's input selection, which is dumb but bites people constantly. I've watched a guy unplug and replug a perfectly good HDMI cable for twenty minutes while the monitor was set to DisplayPort the whole time.
The Fix, In Order
- Reseat both ends of the cable. Unplug from the monitor. Unplug from the back of the PC. Plug both back in and push until you feel it click. DisplayPort in particular has a little latch that doesn't always engage. If you're using a cable with a screw-in connector (some older DVI), tighten it. Don't just wiggle it — actually pull it out and put it back.
- Check the monitor's input source. Press the input or source button on the monitor itself (not the keyboard). Cycle through every option. On a Dell U2419H it's under Menu > Input Source. On an LG 27GL850 it's the joystick button on the bottom. Wait two or three seconds on each input before moving on — the monitor needs time to lock onto a signal.
- Try a different cable. This is the single most common culprit. HDMI and DisplayPort cables fail more often than people expect, especially cheap ones that get yanked. Grab a cable you know works — from a TV, from another desk — and swap it in. If the picture comes up, you've found your problem. Buy a decent replacement; Amazon Basics is fine, no need for a $60 Monster cable.
- Try a different port on the GPU. Your card has multiple outputs. If HDMI #1 is dead, HDMI #2 or a DisplayPort might not be. Use whatever's on the back of the card, not the motherboard — unless your CPU has integrated graphics, in which case the motherboard ports are a valid fallback for testing.
- Test the monitor on another computer. Grab a laptop, plug in via HDMI, see if the panel lights up. If it does, the monitor is fine and the issue is on the PC side. If it doesn't, the monitor's input board or the panel itself is the problem.
- Reset the graphics driver. With the PC running and the monitor still dark, press
Win + Ctrl + Shift + B. You'll hear a short beep and the screen will flicker. This restarts the display driver without rebooting. It fixes the occasional weird handshake failure after a driver update. - Boot into BIOS. Power off, then power on and mash
DelorF2to enter BIOS. If you see the BIOS screen but Windows is black, the problem is your GPU driver, not the hardware. Boot into safe mode, roll back the driver, and reinstall a known-good version from the manufacturer's site.
Quick reference: what each symptom points to
| Symptom | Likely cause |
|---|---|
| No signal on any cable, any port | GPU or monitor input board |
| Works on one cable, not another | Dead cable |
| Works on one GPU port, not another | Dead GPU output |
| Shows BIOS, blank in Windows | Graphics driver |
| Works on a laptop, not the desktop | Desktop GPU or its power |
If It Still Won't Come Up
Check that the GPU has power. Modern cards need a PCIe power cable from the PSU, and if that's not seated you'll get fans spinning but no video. Look at the card — there's usually a light near the power connector that turns on when it's underfed.
Try the monitor on a completely different wall outlet. Sounds dumb, I know, but a failing PSU in the monitor can cause bizarre behavior where the panel lights up but the input board browns out.
If you have a spare GPU, even an old one, drop it in. Ten minutes of swapping will tell you definitively whether it's the card or the monitor. If both test fine separately and still won't talk to each other, it's the cable, every time. Buy a new one. Don't fight it.
One more thing: if you're on a laptop with a USB-C dock, the dock itself is often the problem. Unplug the dock, plug the monitor directly into the laptop's HDMI, and see if it works. Nine times out of ten you need a dock firmware update or a different USB-C port on the laptop.