The potential for damage from another source is increased, but theres no direct and immediate threat from not being grounded. I would definatly make sure your power bar is a good one though.

As for the source of your problems... Still Unknown. The best way to find out is to get hold of another system and start switching parts in and out until something works. As you mentioned that you couldn't do this, you have only two choices I can see:

1) Wait for your system to degrade, hopefully giving you further hints as to the issue. This sucks for obvious reasons.

2) Take it in to your local shop. But problems like these are sometimes simple and easy to find, but often elusive and your tech guy will charge you $70 for nothing.

Spare parts is the best way. Even a spare old crt monitor could tell you whether its your monitor at fault, or the graphics chip on the mobo (likely). Maybe take the HD to a friend and slave it onto their IDE cable for a test copy.