Post a screen shot of your desktop when this happens, in case there is a clue there to see.
When resetting Preferences doesn't take, it is worth having a look at permissions but I thought that was an issue more usually associated with OSX systems. There is a wee bit about permissions and Windows in the Troubleshooting Guide (#13)
You mentioned not having Synergy, but it is worth eliminating any other third party plugins or extensions by starting Photoshop with the Shift key held down (which forces Photoshop to ignore all Plugins and Extensions).
When you reinstalled Photoshop, did you use the Cleaner tool? My gut tells me that your issue is related to Windows _and_ Photoshop, but without a clear idea of what is going on, it is worth being thorough.
Have you tried restarting your computer and having just Photoshop running? Does this happen with all photoshop documents? New documents as well?
I don't feel like I have suggested anything with a strong likelihood of fixing your problem, but this will keep the discussion going.