This forum serves Photoshop.com, an online portal and service, separate from the desktop app. Could you please repost your question here: http://forums.adobe.com/community/photoshop/general
Did you make any changes to you hardware or software between time it worked and not worked?
Have you just tried rebooting program and computer?
Have you reset the preferences? Start PS and IMMEDIATLY hold down the Ctrl, Alt, Shift keys (windows OS). You should get a reset window.