More information needed for someone to help... please click below and provide the requested information
-Information FAQ http://forums.adobe.com/message/4200840
Also, what you describe is USUALLY caused by an automatic Windows update (are you Windows?) that "breaks" something in the graphics display driver as it relates to PPro
So... what is your graphics adapter, and have you gone to the vendor site (NOT Windows Update!!!) to check for a newer device driver
IF you have an nVidia card, How to determine your nVidia driver version
Right click in any open area of the Windows desktop
Select NVIDIA Control Panel from the popup window
Select SYSTEM INFORMATION at the lower left corner
Driver version should be the 1st line in Details
I have a GTX285 using driver 296.10
After a morning floundering about, I finally figured out what it was. I had unplugged my monitor DVI cable last week and for some reason Premiere seems to have thought I was now playing back video on an external monitor rather than the source and program monitors. All I did was turn off the computer, pull the monitor jack and plug it back in. Now premiere is playing back on the source and program monitors.
That was after, of course, rebooting the machine, updating the graphics driver, cleaning the media cache, posting here, and scouring the web for help. Sigh.