Can't open IE after computer sits for awhile -- since installing NIS??

Hi:

 

Seems that this has been happening since I've installed NIS instead of NAV on this computer.  After the computer (Windows XP with a huge hard drive and new ASUS high-speed motherboard) sits for awhile, I cannot open IE-8.  If I re-start the computer, I can then open IE without a problem.  Also the same for a new window after the computer sits for awhile with IE open.  Could this be caused by some setting in NIS?  If not, where can I go for help with this problem?

 

Thanks!