My computer goes on stand by itself

Hmm..CPU temp 85C? I think it's time to get a new CPU fan

By stand by you mean the monitor turns off or it actually shut off? If it's the first one, open control panel and power options. In windows 7 use "change plan settings" and change the "turn off display" to whatever you need. If its the second its the same but change the "put computer to sleep". In windows xp it was also on the control panel and the power options, but I don't quite remember how it was written in it. If it's a laptop and it's turning off because of temperature (the exact temperature changes with different motherboards) then you can check on the bios configuration to see if it allows you to turn that safety measure off. If its a laptop buy a cooling pad or take an old pizza box, cut some holes, put some small fans on it and put the laptop over the fans. If it goes to stand by even when you are using it, then maybe it has a virus or trojan, in which case you will need antivirus software.