Have you tried deleting the Preferences file?
Corrupted preferences file
Photoshop stores your personal program settings in a preferences file...... When Photoshop or Elements starts acting "funny", and does not behave as expected, a corrupted prefs file is very often the culprit. Deleting the file and letting it regenerate is often a cure.
Click here for further instructions: Resetting Preferences in Photoshop and Elements
If that doesn't work, uninstall and reinstall Photoshop, either the usual way through Control Panel or by using Revo Uninstaller
(Pro version is a fully functional trial for 30 days).