Things are goofy now - but it was just fineyesterday. What can I do?

When things start acting weird or not like they should the problem most likely a corrupt preference file. The first thing one should do is trash Photoshops Prefeance File.

To restore all preferences to their default settings:

Do one of the following:
Press and hold Alt+Control+Shift (Windows) or Option+Command+Shift (Mac OS) immediately after launching Photoshop or ImageReady. You will be prompted to delete the current settings.

In Mac OS, open the Preferences folder in the Library folder, and drag the Adobe Photoshop CS Settings folder to the Trash.

New Preferences files will be created the next time you start Photoshop or ImageReady.

You should alway reset the prefs before attempting to reinstall software because it is much less work than reinstalling.

Is one of your tools behaving strangely  or not the way you expect  in Photoshop?

For every tool in Photoshop's Tool Box, the user may choose to fully reset JUST that tool to its default settings. To do this, look up to the Options Bar. On the far left side you will see a button which displays an icon of the currently selected tool. This is the Tool Preset picker. As indicated by the little down-pointing triangle, if you click once on this button a menu will drop down. In the upper right corner of this dropped menu you will see another little triangle, pointing toward the right. By clicking on this button yet another menu will fly out. By scrolling down the list of commands you will see two entries:

* Reset Tool and
* Reset All Tools

The first thing a user should try when a tool is not acting like you expect it should is to apply the command "Reset Tool" from this menu. Often this will cure a problem, and by starting your Photoshop troubleshooting with this procedure you aren't resetting Photoshop's entire behavior and environment to factory default in a wholesale manner. Instead, you're just getting that particular tool back to its default settings, leaving the rest of Photoshop's settings alone. If this doesn't cure the problem you're having, then you may need to move on to deleting/resetting all of your Photoshop preferences to factory default.