You press the power button, the fans spin up, the RGB lights dance, and your monitor proudly announces No Signal. Or worse — No Signal followed by Check cable connection and then the screen sleeps. This shows up most often after one of three things: you just plugged in a new GPU, you moved the desk and re-seated cables, or Windows installed a driver update overnight and rebooted into a black screen. I've walked hundreds of people through this one. It's almost never the monitor dying.
What's actually happening
The monitor isn't broken. It's literally telling you it's listening on an input and hearing nothing. HDMI and DisplayPort are one-way handshakes — the source (your GPU) has to send a valid signal and the monitor has to recognize it. If either side drops the ball, you get this message.
Four things cause 95% of these:
- Wrong input source. Monitor defaults to HDMI 1 but you're plugged into DisplayPort. Common on new monitors out of the box.
- Loose or dead cable. Especially after a move. DisplayPort cables in particular pop out if you don't hear the click.
- Plugged into the motherboard, not the GPU. The single most common mistake after installing a graphics card. The motherboard HDMI port goes dead once a discrete GPU is installed on most desktops.
- GPU not fully seated or missing power. A PCIe card that isn't clicked into the slot, or one missing its 8-pin power connector, will spin fans but output nothing.
If you just built or upgraded this PC, skip to step 3. That's the fix 7 times out of 10.
The fix, in order
- Check the monitor's input source. Press the OSD button on the monitor (usually bottom-right or under the bezel), find Input or Source, and cycle through HDMI 1, HDMI 2, DP, and USB-C. Wait 3 seconds on each — the handshake takes a moment. On Dell monitors this button is often labeled with a square icon. On LG it's under the logo.
- Reseat both ends of the cable. Unplug from the monitor and from the PC. Plug back in until you feel or hear the click. DisplayPort has a small latch — press the release tab to remove it. If you have a spare cable, swap it now. Cheap HDMI cables fail more than people think, especially the thin ones bundled with budget monitors.
- Move the cable to the GPU. Look at the back of your tower. There's usually a horizontal cluster of ports near the top (motherboard) and another horizontal cluster lower down, often with a logo on it (GPU). Plug into the lower one. If your GPU has both HDMI and DisplayPort, try HDMI first — it's more forgiving on handshake.
- Try a different port on the GPU. A dead HDMI port on a GPU is rare but real. If you have a DisplayPort monitor cable, switch to DP and set the monitor's input to DP.
- Reseat the GPU. Power off, unplug the PSU, hold the power button for 10 seconds to drain. Remove the GPU, check the PCIe slot for dust, and push it back in until the retention clip snaps. Reconnect the 6-pin or 8-pin power cables until they click. Boot again.
- Clear CMOS. If you recently changed BIOS settings (XMP, PCIe generation, Resizable BAR), a bad setting can kill video output. Power off, unplug, and either press the Clear CMOS button on the rear I/O or pull the CR2032 coin battery for 60 seconds. Reinstall and boot. You'll need to re-enable XMP afterward.
- Test the monitor on another device. Plug it into a laptop, a console, anything with HDMI. If it works there, the problem is your PC. If it doesn't, the monitor's input board or panel is failing and it's RMA time.
If you're on a laptop with a dock
Docks fail constantly. Unplug the dock, plug the monitor directly into the laptop's HDMI port, and see if the display comes back. If it does, the dock's firmware needs updating — check the manufacturer's site (Lenovo, Dell, CalDigit, Anker all publish dock firmware). Also check that the laptop isn't set to Second screen only. Hit Win + P and choose Extend or Duplicate.
Quick command-line check (Windows)
If you can remote in or use a second display, this tells you whether Windows sees the GPU:
wmic path win32_VideoController get name,status
You should see your GPU listed with status OK. If it's missing entirely, Windows isn't detecting the card — that's a hardware or BIOS issue, not a cable issue.
Still no signal?
Work through these in order:
- Try a different monitor. Rules out the panel completely.
- Boot with one RAM stick. Bad RAM can hang POST before video initializes. Pull all but one stick, boot, then swap.
- Check your PSU. A failing power supply can spin fans but not deliver enough stable 12V to the GPU under load. If you have a spare PSU, swap it.
- Listen for beep codes. Many motherboards beep on POST failure. One long beep plus two short usually means GPU not detected — the manual for your board lists the exact code.
- Test the GPU in another PC. If it also produces no signal there, the card is dead. RMA it.
If you've done all that and still get No Signal, the problem is almost certainly the GPU or the motherboard's PCIe slot. That's a swap-and-test situation — borrow a known-good card if you can, or take it to a local shop. Most will bench-test a GPU for $20-30 and tell you straight.