I've been having some problems with my PC. I'll try to explain.
At some point, my PC shut down by itself. When I try to turn it back on, it doesn't. I have to wait some time before it works. If I do manage to turn it on, Windows is loaded, everything works fine for some time until it shuts down again. One time, before shutting down, a fan (I can't say for sure if it was the GPU or CPU fan) started making a lot of noise. When I try to turn it back on, the power button light turns on but fades quickly and the PC doesn't start.
I tried booting BIOS and waiting, the problem also happened, but before the shut down I noticed that the 12V reading was at ~ 9.9V, sometimes going up to 10V. I read somewhere that this is beyond the +-5% tolerance level.
I don't know what is causing the problem, does anyone have a good guess as to what it could be? Maybe the PSU?
Here are my specs :
Mobo: ASUS P5QL-E
CPU : Core2Duo E8500
GPU : Radeon HD 4870 (HIS)
PSU: Thermaltake Thoughpower 750W
4GB DDR2 Patriot RAM
At first I thought you might have an inadequate PSU, but no 750W should be fine for your system.
I think on those occassions when you do get Windows to boot, the loud fan is quite interesting. It might have been the CPU fan, the CPU may have been overheating, and that may have been due to irregular voltage from the PSU.
If you're going to continue to troubleshoot this it should be with the case open so that you can see and hear which fans may be spinning up. It might even have been the PSU fan itself. The GPU should probably be removed as its non essential. Its removal/disabling will cause a drop in the power draw through the PSU and it would be interesting to see the effects of that.
The PSU may well be on the way out, and they can go with bit of a bang. Be careful. It might be ideal to proceed with a substitute PSU if possible. Make sure its power is adequate, if its rating is lower again removal of the GPU will help. Obviously if another PSU stops the problems, then you know what the culprit is. Could you perhaps borrow one from another computer?
After OR right before? Can't really be both, but I think I now what you mean.
What I was saying is that the fan may be attempting to combat some rapidly developing overheating problem, fails to do so, and the next thing that happens is that the PC shuts down. That would be a logical chain of events.
"If I keep troubleshooting with a potentially broken PSU could that damage other components?"
Yes definitely. At work I have the luxury of a whole load of spare components that I can sub in if necessary. I'm not quite sure what to recommend for someone who doesn't have that facility. As I mentioned before try to borrow a second power supply (PSU) as a test - from a friend or another computer. Check the power rating. I don't know exactly what your systems power consumption would be, but if the borrowed power supply is only say for example 300W, then you can always remove your graphics card to keep the load well under 300W for testing purposes. I'm assuming you haven't overclocked your processor, which of course increases its power consumption.
If you can't borrow a another PSU, then since both me and another poster thought it sounded like the PSU is at fault, you might just take the plunge and order a new one. Before then:
a) Open up your case and make sure everything is thoroughly clean by using an air duster or appropriate anti-static hoover. Particularly concentrate on the case vents; the CPU heat sink; and the power supply. If these are all clogged with dust that might explain your problem, but wouldn't necessarily fit with the dodgy voltage readings.
b) Before buying a new PSU, there must be a PSU section on these forums. Find it, and ask for advice there on an appropriate replacement. Both an over-rated and an underated power supply are not ideal, you need to try and get it just right for optimum running. If the idling load of your computer is less than 20% of the PSU power rating then the PSU will tend to produce excess heat and waste electricity. This is a tweaking thing, but if you are buying a new power supply you might as well get it right.
Oh, I should have mentioned, if you're opening up the case for cleaning unplug the computer first. Then, before touching anything inside, touch the metal case exterior or in some way earth yourself to try and dissipate any build up of static charge you may have.