workstation locks at 2:30 everyday

I have a win98se station. All important info is saved to our network. There is very minimal programs that we run. when computer locks, she has 3things open, outlook200,a dos based program,and media player. Everydat between 2:30-3:30, this stationlocks. I tried doing ctl-alt to see what’s in the background, and found very minimal open. When she tries to send an email, the computer freezes. We have to shut it down by pulling the plug.
Any suggestions?