This is so weird, same thing happened to mine tonight, could it be a dodgy upgrade, are you using XP?
Can't boot even in safe mode, tried all sorts, got the blue screen visible using Disable automatic restart on system failure in f8 and it gave a bad pool caller error
Could be so many things and mine is going back to the manufacturer as its still under warranty.
Only got one 1gb ram stick, so can't take one out to try that and its a netbook so no cd to run a recovery disc (wouldn't recognise an external drive)
Good luck and wonder if anyone else is affected