Computer Restarting, hardware issue i think!

Ok, basically about 6 weeks ago my computer just started to restart whenever i was playing games, then it got worse and started to restart often and during less demanding things. I tried to figure out what was up with it but couldnt, so i figured i'd format the HD as soon as i got home from uni.

When it was restarting there were no error messages even when i changed the settings to where its meant to come up with an error code. It would literaly either completely freeze or just restart itself.

Today i formatted it, it was all going smoothly but then it froze up whilst windows was installing saying that it couldnt copy a file over from the windows disk.
I tried again and it froze at the same point, this time i left it for a while and the computer just turned itself off.

At this point i figured it must be something to do with the hardware right? (please try to bear with me, i'm a complete noob at this kinda stuff)
So after looking around on here people say to check RAM first, i have ran memtest86, but the computer is switching itself off during that too. I've not seen any errors coming up on that while its been running but ive still not seen it do a whole pass yet.

I've also tried doing this with my case open to see if its too hot but that didnt seem to make a difference. It is quite dusty inside the case which i know can be an issue, i'm gonna get a sprayduster 2morro and sort that out and see if it makes a difference.

From what i've said does anyone have any idea what it could be?
If not has anyone got a good idea of how to proceed to figure out what it could be? (please be patient though because i might need things explaining a bit more than most the people on here)

Thankyou in anticipation,
Ben

You're on the right track, checking the probable causes. You just need to keep troubleshooting parts one at a time.

In my signature, there is a link for help with reboots/crashes. Click it. There is a troubleshooting guide there that should help.

Good luck!

What i would do is the following. Get a second HDD ( borrow one if need be ) and install if you can something like Windows 98. If it installs and you can run a burnin test without failure, your HDD is then the culprit. If it still does the same thing, try loading the default bios settings, or take the battery off the board ( after u unplug the pc of course! ) Leave it off and see if the bios soft reset helped. Othewise, follow same procedure with the ram. I know its diff to get spare ram modules or even hdd's, but ask a friend or fellow student to help out.