PC keeps restarting, probably hardware but not sure what

Hi there,

I'm hoping for some help since this is driving me nuts.

For a few weeks my PC has randomly been shutting down and rebooting. I know this can be caused by a lot of things but there are a few things I think I can rule out. I don't think it is a software issue, as there is no error message or blue screen, no new software has been installed recently, and this PC has never been used on the internet so there should be no virus or malware. I also tried a system restore to no effect.

The problem is random and intermittent, sometimes the system will stay on happily for an hour, other times I can't even get it to boot because it just restarts over and over. However, most frequently it automatically restarts after about fifteen minutes of use.

The same thing has happened before about a year ago and the problem was a faulty PSU. Installing a new PSU solved the problem so, since the behaviour was identical, I assumed it was the same problem and purchased and installed a new PSU. At first I thought it had worked since the PC stayed on for ages, but the next time I came to use it the problem was back. It may be worth noting that the startup behaviour has changed slightly since I installed the new PSU - it keeps bringing up a prompt saying "f1 for startup, f2 for bios" and waiting for a response before it goes ahead and boots which it has never done before, and also brings up a motherboard loading message I haven't seen before.

This reaches the end of my PC knowhow and I'm not sure what to try next. I don't mind if I have to replace some part of my system but I don't want to replace the whole thing and I'm not sure how to find out where the problem originates. Any ideas?

System specs:
Windows 7 64-bit
Processor: Intel Core 2 Quad Q9550 @ 2.83 GHz
8GB DDR2 RAM
500GB HD

Thanks!
 
"it keeps bringing up a prompt saying "f1 for startup, f2 for bios" This means that the PC can't find a boot device. Test the hard drive by going to computer. Right-click on the C drive. Select Properties, tools, check now. Put a check in both boxes to set a disk check on the next start up. How old is the motherboard? It is possible that the CMOS battery on the motherboard needs to be replaced
 
Thanks for the response, I've tried the things you suggested. The motherboard and hard drive are both 3-4 years old so it's possible there could be a problem with one of them. I've just changed the battery on the mobo since I had some spares of those batteries and it still shut down repeatedly before I even got to windows so it doesn't seem that was the problem.

If anything my fiddling with things seems to have made the problem worse as I had trouble getting into Windows to initiate the disk check. Interestingly the PC has managed to stay on for the entirety of the disk check though. It has taken about an hour so far so I'm surprised it hasn't shut off, perhaps that is significant?

It hasn't completed yet, I will pop back when it has.
 
Unfortunately it didn't complete the disk check as it shut down right near the end (really annoying). I have started it going again this morning but I'm not sure if it will be likely to complete successfully. There were no messages about any errors during the first check, which was up to about 80% done of stage 5 of 5.

I do have an unused external hard drive it may be possible for me to dismantle and put in the PC and install windows on (never tried such a thing before but I could have a go). Does that sound like it might be worth a try?

Or, any other suggestions I might try to figure out what's causing it?

Thanks!
 
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