Here is a copy of a post I did at the PSP forums about shutting down or locking up. I hope this helps you.
I use version 7 but I was having the same problem. I found out that PSP was storying all my history of PSP in my temp file. It is suppose to delete them when you close PSP but wasn't doing it. Check your temp folder and see if there are lots of files in there you don't know where they came from. The files start with Und(all this is is a history of all your actions you have done to an object. it can't be used once you save a project. It's only use is so you can use my favorite buttons undo and history) . I deleted all these files and then create a separate file for PSP to place these files in. I still have the problem when I keep PSP open all day or it sometimes still doesn't delete the files on close. But now it is easier. When I think PSP is getting sluggish, I just check that file and most of the time it has lots of Und in it, i just say select all then delete.
I hoped I explained this right.

Vivian

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Vivian