I managed to find a post that described the exact same symptons that I'm getting:
After trying everything mentioned and having the same problems:
try to run: sfc /scannow - loads but the load bar does not move
did an AVG virus scan found some viruses but still had problem after.
I'm thinking to do a Mcaffee safe scan as this sometimes finds more viruses.
Can't see anything in Hijackthis, did list shopper reports which I removed and said files were missing so
I guess irelevant.
Norton Ghost's scandisk does not find any physical errors but did truncate some files but still have the problem
What is worse is when I try to login to the recovery console the system at some random time, just turns off
and do not get as far as doing a chkdsk /r
If I try a windows repair it starts to run and again re-boots at 56% of copying files.
I thought maybe a memory error as suggested, so I ran Memtest and left till 41% overall and got tired of waiting
so decided to test the problem by trying EVERY different memory combination e.g. leaving a module out moving it to the other slot etc
I'm considering backing-up, formatting and re-installing but really don't want to.
Hope you can help