HI QF - has yours just occured (as in last night) as well ?
The Norton issue may well be valid - the only machine I have working is not using Norton !!
I have had a couple of Norton warnings requiring the use of an additional scan (forget the name) in the last few days
.... and now all back to life on reboot (previous reboots did nothing).
Only damage done is on my machine where I had reset msconfig etc and generally footled about looking for fix.
Caught one machine momentarily saying 'Norton fixing a problem' - so my guess is a duff Norton upgrade last night and much rushing around and fixing this morning.