Freeserve broadband and Alcatel modem

My system has become unstable since installing Freeserve broadband / alcatel usb modem 4 days ago.

The set up went ok and everything logs on and connects ok but after 20 - 120 mins, the system goes through a short re boot and takes me back to the win xp accounts page.  Broadband zips along but are there any conflict/power issues that anybody is aware of ?