Windows 7 - PC restarts shortly after shut down

[SB420]

Since today, my pc refuses to turn off completely and STAY off. A few seconds after everything has powered off, it just boots back up into Windows 7 like id turned it back on

So far ive tried (with no luck)

System Restore
Flashed BIOS to latest
made sure all "wake on....." devices/features was disabled
Tried turning crash control auto reboot in regedit to disabled with no luck suggesting its not hardware based?
Shouted at it......

and read a zillion threads on google all with no luck.... any suggestions?

 

[F2kSel]

You say you have made sure all "wake on....." devices/features are disabled, is that in Bios or Windows 7.

I know when I had this problem in XP turning them off in the Bios had no effect but in Windows if fixed the problem.

 

[SB420]

Ive turned off all the ones ive found, it was fine till today after some windows updates. Deleting them, restoring etc etc has made no difference and its really puzzling me now