You really haven't given us enough information about your computer or your project for us to be able to help you.
But it sounds like you're using photos primarily as your source footage.
If so, it's likely your problems will all go away if you resize your photos to no larger than 1000x750 pixels, per the FAQs to the right of this forum.
If that doesn't fix it, then we'll need to help you troubleshoot your comptuer.
Version 7 is a very stable product when used with optimized source files.
Thanks for the reply... Yes, I am using still photographs inported thru a file saved on my computer. I will read the thread you posted, see what happens and then let you know!!!!!
Is there a way I can re-size the photos that are already in my project? I have so many photos already placed and in order and I would hate to have to re-do the whole thing....
To my knowledge there is no way to Re-Size photos already imported into PE.
Your only option is to re-size outside of PE, then re-import.
As Steve stated, this most likely is the cause of your grief, once the re-size changes resolved, it should be (relatively) smooth sailing...
Unfortunately, once you have Imported the images, one needs to re-Import the resized images.
Now, I have had luck by replacing Imported files with different ones, from the same folder and with the same name.
Let's take this step-by-steop:
1.) In your original Project, do a Save_As, and maybe add "test" to the file name, or locate it into a totally separate folder. We want to work with a new version of your Project, and not the original. Close PrE.
2.) In Windows Explorer/My Computer, navigate to the folder with the large still images, and Move them to a working folder. Do not Move, Rename or Delete the now empty folder, where they were. We're gonna' fill it with the resized images in a moment.
3.) Look over this ARTICLE on automating the Scaling/resizing in Photoshop (PS) (most works just fine in PSE too). What we want to do is set the images that we just Moved, as our Source Images/Source Folder. We want to make sure that the file names do NOT change, and that the Destination Folder is our now empty one - where the Source Files were just Moved from.
4.) When you have resized all of your images to match your Project's Frame Size, and filled that original folder with those, with the same file names as the originals - the ones we Moved, launch PrE, and Open your "test" Project. Since you still have the same links, the same file names and the same location, the resized images should come into your test Project. In case things go very wrong, just Move the resized images out, leaving the empty folder again, and Copy, or Move the original large files back into it. Now, you can use your original Project, the one that we held onto for safe keeping.