Pc switches off at night.

Hi all.
Three of us use this unit in the house and over the last week or so it has begun to shut down at night without us changing any settings.
I need it to stay on during the night as I upload photographs to a colour correction company via FTP regularly (wedding photographer).
I asked the other guys if they have installed any new software but the response is just shrugged shoulders. The antivirus is avg free and zone alarm is active but they have both been running for a very long time now. I run malwarebytes periodically and do the defrag thing every two months or so.
I have also noticed the desktop refresh itself more than usual? Related? I have no idea. Also the fan on the power supply is begining to labour a bit. When I boot it back up there is no 'windows serious problem' message. Its just as though it was powered down normally.
My sincerest apologies if I am not making sense. I have a hijack this log waiting to post if this would help.

 

You didn't specify your OS, but the first thing I would check is your "power options" .
Start>control panel>power options . Check your plan settings to see if your computer is set to turn itself off after a period of time of inactivity .

 

Power options all fine and set to never. Its XP sorry.
Its as though something other than windows is scheduling a shut down.

 

I tend to think that it is overheating, as it gets a lot of use, and shutting down overnight while your photo work is happenning, fan labouring on the power supply...
Have you anyone capable of giving the pc a spring clean, for dust and fluff ?

 

Tesla,
I too, keep my laptop on 24/7 (use a magicJack & do a lot of timeconsuming grafix downloads at night.)
My laptop has been turning off, seemingly of its own free will as well. Finally decided was an overheating problem & tho I now have a fan flowing directly ON my puter, plan to invest, asap, in one of those "cooling systems" one can rest one's 'puter on (so I can use my fan to cool *ME*, instead.)
Also neeed remember one's ADAPTERS, too, get hot (especially in summertime). I moved mine so the fan is now blowing on both my puter AND adapter.
Hope this helps...

 

You can also check the event viewer to see if there were any entries around the time that it shut down that might give an idea why.

Start->Run->eventvwr