No problem Tonks... there are logs... not brown ones, but flight logs for the computer. After it does it next time, as soon as you start it back up, go to
Start> Then right click where it says "My Computer" and select manage.
In the right hand pane of the management screen, expand "event Viewer" then "Windows logs" Then click on system.
The first event recorded when the system starts up is "Microsoft (R) Windows (R) 6.00. 6000 Multiprocessor Free." This is an informational event with Event ID 6009.
the entries preceeding this one tell what the computer was doing when it went TU.
Check the application logs arround the same time, as they may indicate if an application was causing the fault.
Let us know how you get on.
