I have a lenovo pc running windows 7 and only is used to run a digital signage program which displays on a TV. The program will run when I start it at 4:30 am and will run constantly all day. We close at midnight and it is still running. At some point between midnight and 4;30 am again, I come in to work to find the computer at the login screen. I log in, the signage program starts and the same process happens again. I have removed all evidence of sleep mode, never turn off hard drives, monitors. I've checked the event log and nothing seems out of the ordinary. What would be causing this, and how can I prevent it from logging out or am I missing something?