Computer Shuts Down automatically at night!

That's not a bug; it's a feature.  

If it's not software, it's got to be hardware. What kind of PSU?

hmm 300W PSU, i guess its not a problem because in morning hrs it does not shutdown...my PC is on for 5-6 hrs in morning but no problem.

I think it shuts downs when PC is in idle but in power options i have disabled going to sleep or hibernate.

300W is probably not enough, even with a 9400GT.

Care to post any other specs or brand of PSU?

Despite it being a hardware problem as suspected would it be helpful to restore the system to a date just before this started occurring? If nothing else it might help rule out possibilities and support others.

I wish I could be of more help but I had a heck of a time with trying to allow my old vista system to hibernate upon command. So I had a similarly frustrating experience but under opposite end goals. It was a lot of reading among forums and how tos on Google that got it fixed for me.

if it was a PSU problem, then my PC would shutdown even during daytime when i use it cotinue for 5-6 hrs.

So i think their is a problem were it shuts down when it goes in idle mode(when i dont use it for 7-8 hrs)..i think

i will try to use XP for a day...hope for the best