Computer shuts itself down

Ive been having a bit of a problem with a vista os taking forever to load on startup, poseted in HERE Last week I was able to leave computer running for several days without it shutting itself down. It worked ok. Since this weekend, If I leave it running overnight, it shuts itself down every night. Im trying to run an online storage backup and not sure if Im having a harware issue or not. Is there any log I can run to see what is causing it to shut itself down?
Like I said before, last week it ran an online recovery for like 3 days straight with out shutting down. Now I can't seem to get it to run overnight without shutting down.
Thnak you for any suggestions.

 

I believe you should look into the possibilty of the pc overheating, Take sidecover off and have a look inside, heatsink could have built up dust,lint whatever else you can think of blocking the cooling effect of the fan that sits atop of the heatsink. ed

 

Thanks Tunered. I checked my bios and the cpu temp was around 56 degrees C. I took cpu fan off and re applied thermal paste, buttoned her back down, and started up and checked bios temp and it started at 60 degrees C and climbed to 71 in a matter of minutes. Is this temperature too high?
I called EVGA and a tech support guyt said it should be below 50, and a local techie said anything below 80 is ok. I have had conflicting info from evga tech support in past. Should it be below 80 or 50? and why would the temp climb back up after thermal paste is applied? The fans are working.

 

Have a look at the event logs:

All windows versions:

Right-click on "My Computer", choose "manage" and then click on "Event Viewer".

Look through the logs and see if there is anything pertaining to system failures etc.

 

Even 56 cel. is high, in the 40s is somewhat the norm, even tho the cpu fan is turning it may not be turning fast enough. When temps get extremely high the cpu fan should kick into high gear, this you should hear. ed

 

Thanks guys. I looked at logs and didnt see anything about system failures. I just booted up system and it says cpu temp was 59, now its 48. Motherboard temp is 30. Im using everest to monitor temps while Im working.
How would I check to make sure the fan kicks on high? Is there a bios override setting that may be set too low?

 

When you first boot you should hear the fan run on high just for a second, if your temps stay where they are dont worry, some motherboards support speedfan which lets you determine fan speeds,

http://www.softpedia.com/get/System/System-Info/SpeedFan.shtml