More information needed for someone to help... please click below and provide the requested information
-PPro Information FAQ http://forums.adobe.com/message/4200840
And, exactly what are you editing?
Codec & Format information, with 2 links inside to read
-read both links in reply #1 http://forums.adobe.com/thread/1270588
Report back with the codec details of your file, use the programs below... A screen shot works well to SHOW people what you are doing
Welcome to the forum.
I completely agree with John T.
The more information that you can provide, the easier it will be for others to help you. His links contain several very important questions, and your answers will be very, very important.
Good luck, and please let us know quite a bit more about your PrPro, your computer, your Sequence settings and your Source Footage.