Hi Fred,
If you haven't already done so, try trashing the Finder Preferences and rebooting; also, try rebuilding the "desktop file" at system startup.
In addition, I guess it wouldn't hurt to run a disk diagnosis/repair utility on your hard drives -- e.g., Apple's own Disk First Aid 8.5.5, or a third-party tool such as DiskWarrior 2.0, TechTool Pro 2.5.x or Norton Utilities 5.0.x.
Good luck,
--Paul