What are your Project Settings? You'll find them under the Edit menu. In version 10 you MUST set up your project manually to match your video specs, and if it's not matched correctly, the program will not function efficiently.
Is there a yellow line along the top of the timeline, above your clips? This means that your timeline must be rendered. Press the Enter key on your keyboard and see if performance improves when this line turns green.
Photos should not cause problems as long as you've sized them all to no larger than 2500x1875 pixels in size (72 ppi). Have you done this to all of your photos and graphics?
Version 10 also does not mix video sources well. You say that some of your video is a gameplay clip. You may need to crack open one of those clips with the free download Media Info in order to determine its resolution, frame rate and audio video codecs. Version 10 is not going to work well with non-camcorder standard video frame rates or codecs.
What type of video is the majority of your project made up of? What model of camcorder is it from and what format and resolution is it?
Prior to version 11, Premiere Elements was very limited in the mix and format of video it could work with.
Project settings are 1920x1080, square pixels, no fields, 30fps drop-frame timecode. I haven't made any changes to those.
I regularly render the timeline, even more frequently with this project because it's running so slow.
All of the stills are definitely smaller than 2500x1875.
Most of the project is gameplay clips, some is shot on a Canon Vixia HFR500, all at 1080p in MP4 format. The gameplay comes from my El Gato capture card. Most of it is at 720p, some is at 1080p. The El Gato software gives options for how to encode it, but I've always used the MP4 option there as well.
Again, what's really getting me is that this is part of a series I do, and I've done numerous episodes with Premiere Elements 10, but this is the first one to cause trouble. I even went and loaded up the project files from recent episodes and could move around clips, add clips, etc, and it didn't cause the program to start moving like molasses. It's weird.
UPDATE: Just to illustrate my point, I just opened the project to get the project settings for you. The entire timeline is rendered, and I couldn't do ANYTHING in the project. Just clicking the X to close the project didn't respond. I got the "Premiere Elements is not responding" error and had to force close it. And literally all I had done is open the project settings, then close them and try to X out of the program. In contrast, last night the last thing I did before posting here was open an old project (this is the final product, for reference: Same Name, Different Game: The Adventures of Batman and Robin - YouTube) and it gave me no problems whatsoever. I even added new clip to the end of the project, moved it around, resized it, etc, just to make sure I wasn't crazy. I'm so baffled.
I'm surprised to hear that Premiere Elements 10 hasn't given you problems with previous projects using gameplay clips and MP4s as your source video, shakewell. As I said, version 10 is relatively primitive, as far as working with various video sources goes. Since version 11, the program is much more versatile. I don't even know if version 10 can edit MP4s natively. You'd do much better to shoot your Canon video in AVCHD -- or a consider a move to a newer version of the program.
Interesting. I will change the settings on my camera for sure. I also didn't realize I was four versions behind, so I may just upgrade to the latest (unless you think 11, 12 or 13 is better for some reason). But I appreciate your help!
UPDATE: Thanks again for the assistance, but I do need to report that the issue was apparently the length of the gameplay clips. I confirmed that they were all around the same length as what I'd used before, but it was rare for me to have clips that went over an hour. I used the game capture software to cut the clips down into ~30 minute chunks and we're good. The program is not choking to death anymore! Huzzah!
Thanks again, Steve, for helping and being patient. I really appreciate it.