Not much info to go on - but try this:
Download this free application: ShellExView - Shell Extension Manager For Windows
Disable all non-Microsoft extensions
Reboot to see if that helps (if not, don't forget to re-enable them).
If it does, then disable them in groups of 5 or 10 until you find the offending group
Then do that group one at a time until you find the offending extension.
Uninstall the program related to that extension and (if you want to) install a freshly downloaded copy to regain that funcitonality.