|Thanks for your responses guys.|
I'm not sure what to make for the event logs. There's errors for IPNATHLP, Dhcp, W32Time and System error but the chronology doesn't always match.
I think now that the Symantec message is an effect of rather than a cause of the failure.
Othehill, i was wondering why a disk cleanup is advised, on top of the normal anti-virus procedures, in relation to this issue. ie what it does that your AVG's etc don't.