Hopefully someone can shed some light on this as I'm very confused.

Here's my system spec first of all:

XP Pro
P4 3Ghz CPU
512 RAM
Asus P4S800 mobo


And here's the problem:

For a while now, every time I try to turn my PC on, it'll beep (the normal beep that usually happens when it's turned on), the power and hard dsk lights come on on the case, the fans start up BUT only for a fraction of a second (well 0.5 to 1.5 secs, it varies). So it's off again, and to try and turn it on again, I have to unplug the power cable from the back of the case and plug ti back in otherwise it stays dead. This happens anything from twice to 30 times before it will turn on properly again. Then it'll work absolutely fine until I turn it off and onm again, where it might take from 5 minutes to 3 hours to get it to turn on again. Another thing I've noticed is that if I unplug the power cable from my C: drive the computer turns on first time every time (obviously I get the "system disk could not be found, plug it in and press enter" error or something to that effect).
I have no idea what it might be. If it was the power supply surely it wouldn't turn on and especially stay on ever would it? although the fact it boots fine when the hdd power cable is pulled out would point to some power thing...
I've tried unplugging the power to the dvd drive but that makes no difference. I've tried it with all my PCI cards taken out but that didn't make any difference either.
Could it be heat? I have had problems with my CPU getting too hot but I've now got the side panel off and I try to clean the dust out of the CPU fan every so often and I haven't had any problems with that for a while.
If anyone has any idea what the problem to be I'd love to know. I'd rather not spend £20 for someone to have alook at it if it's something I can easily do myself...
Cheers

Hello and welcome to PC Help Forum!!

That definately sounds like a power supply issue. Get the computer to boot successfully, and then do this:

Please download Speed Fan and install it.

Start Speed Fan. When it is fully loaded, take a screen shot of the first screen by pressing Print Screen/SysRq on your keyboard. Open Paint and paste. Save the screenshot as a JPEG and post it in a reply to me. Now click on the tab called S.M.A.R.T.. Select your hard drive by using the drop-down box at the top. Now take a screenshot of that as well. Post it in your reply to me as well.

NOTE: For certain computers, Speed Fan will not display accurate measurements. If the temperature wildly fluctuates or doesn't change at all, let me know, otherwise I will believe the mesurements are accurate.

thanks. here you go:

Your +12 voltage is an entire volt off. That is beyond the .5 tolerance. And considering the symptoms, I'd be willing to bet that that's it.

However, there's a few things we gotta take into consideration. Here's a little important info, though if it's too long, you can skip to my short summary at the end :

Testing your power supply with software will typically give incorrect readings. There's one chip on the motherboard that manages health monitoring (typically referred to as the "Winbond chip" because the chip is typically made by Winbond.) The margin of error on this chip is pretty great because it needs to be taken into consideration where this chip gets it's data (the ATX connector) and the resistance created by the traces between the ATX connector and the chip.

Software isn't COMPLETELY useless however. If readings are WAY OFF, there may really be a problem with the power supply. But always double check the ATX connector to the motherboard first. If for some reason the connector is not plugged all of the way in the board, the resistance from the loose connection can cause low voltages.

If the connections are good, and you'd like to further test the power supply to make sure it is bad, you are going to need an electronic device called a multimeter, (more than likely a Digital Multimeter, or "DMM" as it's referred to here) which you will physically have to plug into the connectors on your power supply.

My Summary
Open the computer and check your power connections to the motherboard and all the other devices. Make sure they are firmly in place. If they are good, then the power supply is probably going out. If you'd like to test it further, you'll need a multimeter, and I'll give you a site that explains how to test it. Otherwise, I'd buy another power supply that is identical to that one.

Yep have to agree with computerwiz.

thanks very much for the replies. sorry i didn't reply sooner.

another development... someone else suggested i tried the power cable from my cdrom drive to power the c: drive. i don't know why i hadn't thought of that earlier but anyway... i did that and turned the pc on. the first time i smelt a slight burning smell. i turned it off and had a look around but couldn't see anything and couldn't tell where it was coming from.
i tried to turn it on again and it turned on fine first time. for the next few days it turned on first time every time but then started to play up again (exactly the same problem as before). Since, it just seems to be getting steadily worse again (taking more and more tries to turn it on).
I took out my stick of ram the other day and noticed that there was a slight burn mark on part of the connector. I'm assuming that's what the burning smell was. Computer still works fine once it's turned on though...
Does any of that help at all? Any more ideas?
I suppose the next step is to try a new power supply really...

hello nematix and welcome to pchf

if your ram has burn marks on it you will need to replace it and i would also buy a new power supply

genie3251