Are you able to open an older autosave version of the project?
I am with John T. here. I would launch PrE, and at the Welcome Screen, choose Open Project (the AutoSaves will NOT be in a list yet), then navigate to where that Project is, on your system. Within that Project's folder, will be a sub-folder, AutoSave. Try to Open the latest one of the five (the default) AutoSave PREL files. Note: AutoSave files are FIFO, and each will be overwritten, over time. That means that file #3 might be newer, than #5. Just check the Date/Time of the files, and go for the newest, working back to the oldest, if you have issues Opening the newest/newer one(s).
It might actually be easiest to first look in that sub-folder in say Windows Explorer (or Finder on a Mac), and make note of the Date/Time for each.
Thanks for the replies. Yes, I have tried to open the autosave files. I apologize for not mentioning that in my original post. However, I get the same result. The loading screen will stay at 100% for as long as I leave it there. Is it possible that my media window has too much footage in it? I am working on two projects at the same time, but I wasn't sure if I could delete clips from the media window without error before completing the project. It's just strange that all other projects (some larger than the one at hand) open fine. The files in said project are rather large because I filmed in 1080. I don't know if that has anything to do with it.
OK, there is possibly a problem with one (or more) Assets.
This next step might be easy, or not, depending on how you have your Assets arranged on your computer.
The easiest is if one has the Assets, or Copies of them, in sub-folders below the Project's hierarchy. See this article for an example: http://forums.adobe.com/message/4028199#4028199
I would Move the Assets from their location, so that PrE cannot initially find them, and attempt to load their links. Then, launch PrE, and Open that Project (since the AutoSaves do not work better, just go with the original Project here). You should get the dialog, "Where is file ____ ?" See this article for more details and tips: http://forums.adobe.com/message/4598705#4598705.
If one has many types of Assets, such as Still Images, AVI's, MOV's, etc., it would be easier if one Moved each Asset type to a new, and separate sub-folder, for this next step.
At "Where is file ____ ?" navigate to where you Moved that requested file. See if it loads. Per the above article, you will see that PrE will then survey that folder, the one that you just navigated to, and try to load each missing Asset IN that folder, and re-link to them. If all goes well, then you should get that same dialog messege for the next Asset type. Repeat. Do this until you get the hang on an Asset. At that point, DO NOT Save the Project. Instead, Save_As and increment the name. That is IMPORTANT.
Then, Move that faulting Asset elsewhere, and test Opening the Save_As Project. If all works fine, then you know that there is a problem with THAT Asset. You should study it carefully, to see what the problem is. If it plays fine elsewhere, and is not different, than other good Assets, then try Importing it again, into that Save_As Project.