Hi mac, most likely your preference file got corrupted. Toss it out, Photoshop will make a new one when it's launched again... (Prefs.psp - located in the Documents and Settings/[user profile]/Application Data/Adobe/Photoshop/[version]/Adobe Photoshop [version] Settings folder) not sure if you're WIN...

OR

reset your Photoshop preferences by holding down the Shift-Ctrl-Alt as you launch Photoshop.

let us know if this helps,
:)
retrocity