Just recently I upgraded a friends computer to Windows 7 from Vista. It was really slow and clogged with random background tasks and it seemed like the best option at the time. Anyway, she just told me that now when she turns the laptop on and logs into her account, it logs her back off and shuts down.
Specs (as far as I can remember):
Intel Celeron(?) dual-core @ ~2.4GHz
Windows 7 32-bit
The laptop is between 3 and 4 years old. I only installed Avast and OpenOffice on it last night and it wasn't doing any of this. She also never turns her laptop off if that has any bearing on the matter. I'm having her run the Windows 7 diagnostic stuff right now so I will post later as to what she finds. Sounds to me like a memory error?