Hi Scott,
I have had this happen to me when I have been installing and uninstalling different versions of ArcPad.
My advice would be to do a full uninstall of ArcPad and then perform a fresh install of ArcPad.
It is possible that some of the folders (eg. the icons folder) that were installed by ArcPad have been moved/removed.
Have you re-mapped your My Documents path recently? Are you logging onto the machine with a different profile?
Let me know how you get on,
Hannah