soens
Last time this happened I did a System Restore To An Earlier Date which solved it.
Despite your statement that the system is not on the internet, unless you can rule out the possibility of a virus 100%, this does seem to suggest a dormant virus -- one that's likely to be resident on your current Paragon image as well.
And if it is a virus, my guess is it's a Rootkit or boot-sector type... which means that Norton (or most any other mainstream commercial antivirus app) will not be able to detect or clean it. Nowadays, you need at least 3 or 4 different cleaner apps to have a decent chance against some of the more sophisticated viruses.
For starters, Kaspersky has a free Rootkit cleaner you can download from their site. Easy to install and run...
If it were me, I'd restore from the image, and then before doing anything else:
-- Wipe and recreate the master boot record, using either a dedicated utility, or FIXMBR command.
-- Scan the C: partition with at least two good anti-malware apps, in addition to a dedicated rootkit scanner.
Assuming it's a virus, the above should give you a fighting chance. And even if it's not, these steps won't hurt anything (other than being time-consuming).
Good luck.