One other thing:
Event viwer seems to log the following error message under 'applications' everytime my laptop switches itself off:
The COM+ Event System detected a bad return code during its internal processing. HRESULT was C0000005 from line 44 of d:\qxp_slp\com\com1x\src\events\tier1\eventsystemobj.cpp. Please contact Microsoft Product Support Services to report this error.
No idea if this would have anything to do with it though.
I've looked on MS knowledge base and not found anything useful.Interetingly the crash seems to happen much more frequently when I play Virtua Tennis (i.e. every few minutes).