Hi gang
well i have a pc tower in and it is doing random shutdowns and then restarting
it is not a brand pc it is a bitsa (bits of this bits of that ) lol

we have done a deap virus scan " all clear"
we did a defrag
drive usage is not over 80%
oh and i gave it a good dusting out so it is dust free for now
It always seems to occur when on facebook

did i say its my wifes computer so it has to be done a.s.a.p ...... lol

What about your system temperatures. Random shutdowns are usually an indication of an overheating CPU.