Auto disconnnect

The user in Win95 log on to the Nt4.0 server everything will work great for 2 or more hours and then her computer get disconnected. I can see other computers on the Network but I can not access the mapped drives it ask for the password.
On the NT server event viewer shows that the user logged off but she did not. How can I fix this problem. His my server going bad or am I doing some wrong? I can find any fix for this problem anywhere.

Thanks for your time.
Regards

Hecas