I have a Dell PC(Optiplex GX 280). I use it to run a process which takes about 4 hours. Is there some way to have my computer automatically turn itself off in 5 hours? Is there such a thing as a PC sleep timer?
The simplest thing might be to set up Power Options (in Control Panel) so that your computer hibernates automatically after 5 hours idle. That'll do a full shutdown, with the added benefit that when you start up again, everything will be as you left it. (Would suggest closing any open Office files first, though.)
Remember to check the hibernation tab first, to confirm that it is enabled.