Have you rebooted your pc yet? Sometimes Windows decides that it knows best, and does whatever it feels like. This could be one of those times. Reboot if you have not done so and see if that fixes the problem.
If it doesn't fix the problem, I sugguest that you run all of your anti-spyware/virus programs in both normal Windows and Safe-Mode Windows and see if that pulls up anything.
As to the ShellIconCache, I wouldn't fool with that just yet. If you delete it, it is liable to make Windows mad.