You've posted to the Premiere Elements forum. While there are some here that use CS5 you would reach a wider audience in the Creative Suite forums: http://forums.adobe.com/community/creativesuites
Insanity is hereditary, you get it from your children
Thanks I wasnt paying attention
Before you go there, be ready to answer lots of questions
Work through all of the steps (ideas) listed at http://ppro.wikia.com/wiki/Troubleshooting
If your problem isn't fixed after you follow all of the steps, report back with ALL OF THE DETAILS asked for in the FINALLY section, the questions at the end of the troubleshooting link... most especially the codec used... see Question 1
Read Bill Hunt on a file type as WRAPPER http://forums.adobe.com/thread/440037?tstart=0
What is a CODEC... a Primer http://forums.adobe.com/thread/546811?tstart=0
What CODEC is INSIDE that file? http://forums.adobe.com/thread/440037?tstart=0
While you are gathering the info needed, for when you post to the CS5 forum, this ARTICLE might prove useful.
Also, please update your video card's driver to the very latest version. If you have an ATI, note: there were some fairly recent versions of the ATI Catalyst drivers, that did not work well with Adobe programs. Many users found that they had to roll-back a few versions. I would assume that by now, ATI/AMD has fixed that, but keep that in the back of your mind.