Solved Black screen/monitor goes to sleep minutes after powering on

A matter of minutes or even seconds after powering on, the screen goes black. There is a "no signal detected" message is displayed. That is to say, the monitor has gone in to sleep mode. Sometimes a slightly louder whirring noise can also be heard for about a second or two before the monitor goes to sleep. No idea exactly which component is making the noise. From what I can gather, everything else seems to function fine after the monitor goes to sleep.

This is not a Windows problem as it has also occurred whilst in BIOS.

I first started getting the problem a couple of weeks ago. There were no major recent hardware changes other than the replacement of some frustrating Microsoft wireless keyboard with a generic PS/2 keyboard -- which I have reliably used in the past with no problems whatsoever.

Hello dyvrnaix. Welcome to the Forum.

Is this a desktop PC?
If so, is it an all-in-one type?
If it's a typical Monitor and box setup, does the whirring sound come from the box (computer case) or the monitor?

Sorry for the confusion. It's a desktop; typical case and monitor setup. The sound is coming from the case.

Ok, thanks. I've got a picture now!

When you get a no signal detected message on the monitor it means there is no output from the video card. And since this also happens in BIOS it indicates a problem with the card (or on-board graphics chip if that is the case).

The whirring sound is most likely a fan. It would be very helpful to know what fan is speeding up: the one on the video card, the one on the processor, or one of the case fans.
You can check by removing the side of the case and observing (listening) as you use the PC. You can also use a short length of plastic tubing or cardboard tube to your ear to isolate which fan is speeding up.

The other whirring component is the spinning hard drive. So listen for that too.

Also, observe how much dust and stuff is in the case and coating the components.

Let us know what you find.

Note: use proper static precautions! Do not touch or move parts while the PC is on. Only use non-conductive tubes - never metal.

I have a separate graphics card. From memory, a fair amount of dust has accumulated since it hasn't been cleaned since I bought it in mid-2009 (oops, my bad!). I was planning to buy a can of compressed air from wherever, and give it a good clean soon anyway. Thanks for the tips, I'll try listening out for and isolating the noise tomorrow.

Good plan!

Many video cards have thermal protection, so they will cut out if they overheat. So if the fan on the video card is spinning up then that may be all it is. Cleaning the dust out of the card may solve that.

Let us know what you find.

Well I gave it a pretty good clean, but the problem still occurs. It's also really difficult to isolate which fan the noise is coming from.

Well, let's focus on the video card then.

First, re-seat the card. With the machine off, take the card out, check the slot and blow it out for dust, and replace the card.
Reconnect the cable, at both ends, and check the cable for defects. Try another cable.

Another cause of a problem like yours could be a failing power supply. Check the auxiliary power connections and/or use another pair of connectors.
If you have a multimeter you could test the 12v during boot to see if power is dropping off as the computer starts.

Let's see what that does, if anything.

Well, I reseated the graphics card but that didn't seem to do much. I did discover, though, that there was quite a bit of dust on the graphics card in places I could not reach easily when I was dusting everything yesterday. See: http://img440.imageshack.us/img440/4915/20121111004107199038333.jpg . I didn't think to take the graphics card out yesterday, but now I know better -- I'll have to buy another can of air soon and clean the bits where I missed.

The good news is that I did end up fixing the problem -- my machine's been on for about 35 minutes so far (typing from it atm), whereas before I could barely two minutes use out of it. Unfortunately I don't know what the problem was exactly, as I replaced the cable leading to the monitor AND I used a different auxiliary power connector that happened to be unused inside my case, and only then did I test to see if it worked. I have my doubts it was the DVI cable's fault, but I'm in no rush to start pulling my computer apart again to try and isolate the problem cable/connector though. In any case, thanks for all your help!

It doesn't really matter - it works!

It was probably just something loose or corroded (the contacts on the connectors can oxidize) and re-seating is what takes care of that. People like to think that there is a final answer for these things, but most often it is just a matter of throwing everything at it and see if something sticks. That's why slapping the side of the TV was always such a time honored repair method.

And clean that video card! Yikes. Always a good idea to keep some compressed air around anyway.

Happy computing.