Toshiba Tecra S1

I have a Tecra S1 that I’m having problems with. If I leave my laptop idle for a while when I come back to it it won’t respond. Only in the window that was left open can I do anything. Programmes won’t open and I can’t shutdown unless I keep the finger on the off button. I’m runing Win XP SP1 on a Novell network. Can anyone help?