xp home with sp1.[oem]

no problems until 3 days ago. now =

system restarts when switching user
system restarts when accessing video file [avi/etc]
system restarts when playing audio files [mp3]
cannot restore system to previous date
cannot encode avi to dvd format [vob] - NAV file created instead of BUP

device manager shows alert for:-
Basic System Device
ATM Network Controller

cannot reinstall/locate either.

help/advice more than welcome