Lots of good and useful info everyone - thanks!
The Anti-Malware software identified four Trojans on the drive and removed them. AGV confirmed there were no other issues. However, the virus did leave behind some permanent damage that I can't fix so I will be trying the Dell restore approach.
To answer some questions - I found out I had a virus when the AVG window popped up and I misfired on the mouse and accidentally clicked Ignore instead of Delete the virus (or whatever the exact terminology is). Most of the icons on the Desktop disappeared, leaving the default symbols in their place. Double clicking on one of these would briefly open (appears as a flicker) a DOS text box that said something about an error in the command line. That's all I could make out, even with repeated viewings.
Interestingly enough, clicking on a data file, I can open the associated app. Click on a doc file and Word will open, for example. I was even able to work on a piece of music in Sibelius, although I can't print. I can Export to PDF however.
I've made plenty of mistakes in this process, but I've been able to copy everything (except the Windows directory) from the System drive to a brand new HD so all my data is backed up. I'll reset with the Dell partition and move pertinent data back over.
I've also picked up a copy of Norton Ghost that will be installed post haste to set up a back up routine. The good news is that nothing has been lost except time, and that's not totally crucial this week, thank goodness.