XP reboots when dialing up

I recently flashed my BIOS to the latest version. The only problem I had was with the autodetection of my HD. I had to put the details in manually and all seemed fine. I was able to use dialup after the upgrade until recently when trying to dialup my ISP it immediately reboots my machine. Can’t understand what might suddenly have changed to cause this problem. Not tried reinstalling the driver yet but can’t see why it should be OK one minute and Kaput the next. Any ideas