Going into sleep mode when trying to install windows

Friends recently received a free Dell 650 that was supposedly "cleaned". They asked if I would install windows and set it up for them. However, the first time I tried to install the computer got about half way through and then just went into sleep mode. Keyboard lights went out and non functioning, monitor went blank, tower light stayed steady green. I would allow me to open and close the cd door. Shut it down and when I turned it on it started to resume install, after about 5 minutes it went to sleep again. Shut it down and tried again, this time it only got to the blue windows install screen when it back to sleep. Does anyone have any ideas as to what the problem could be?