Sorry for the long post but I am now thoroughly confused.
This morning it did it again. I was gonna go into event viewer and see if there was anything suspicious in there, so I was about to type my password in when the computer went into a restart loop. It would occasionally get as far as the bios screen and sometimes would just spin up and then go off again. I then cut the power at the wall and removed components one at a time to see if I could isolate the problem.
The problem was still there with the IDE cable for the DVD drives unplugged and also with the unnecessary PCI cards removed. I then unplugged the HDDs, front panel switches and one stick of RAM and now it boots fine, even with everything plugged back in.
So now I'm thoroughly confused as to what could have caused it.
I also looked in event viewer and couldn't see anything suspicious but I don't really know what to look for so if there's anything specific I should be looking at could someone let me know
Thanks