I will try that but I pretty much doubt that it is a PSU issue. If I use my old HD with XP installed the computer shutdowns normally.
Hmm hate to disagree polanskiman because the 3.3 rail is way out of whack as is the 12v rail in all honesty I am wondering how the machine is working at all.
I think like a lot of other folks the importance of maintaining a the correct voltages for the running of the machine is too often overlooked.
Now if you read that link to tomshardware I sent with the HW Info post it will tell you just how important it is and in particular that the supplied voltage must be within 5% +/- (positive / negative) of the voltage it is supposed to be. Some simple maths will show you how out of whack your voltages are.
For example a 12v rail should be at the very minimum 11.6v and maximum of 12.6v so in effect your 12v rail of 11.28v is really quite unacceptable and likely to be the cause of a lot of the problems.
There is also the issue of the Power Good signal - also in that link please read it - the author is a very well known and respected technician. It in itself may well be the cause of the shutdowns.
As you may know components these days run within very fine voltage tolerances and it doesn't take much imagination to see that any slight variation is going to throw things out of kilter.