What icons did you change? If you change them back to the default, does it make a difference? If not, I have two suggestions:
1. Use System Restore to go back to sometime earlier in the week. Your files won't be deleted, but you may need to reinstall some programs that have been installed recently.
2. Download
CCleaner (install without Yahoo! toolbar) and clean out your temp files and registry (be sure to backup). Then download
AVG Free, update it, and scan in Safe Mode.