Have you considered that you may have your computer accidentally set up for multiple desktop support? You should check Display options to ensure that the optimum resolution is being used and that only one desktop is active on the screen. If you can remember when the problem started, this could give you a clue to what is causing it. Check for the latest driver updates for your graphics card, whether integrated or PCI, or even consider reinstalling them.
Check the Display options to make sure that only one desktop is appearing. In the case where multiple monitors or desktops are configured, application windows will have a tendency to be moved to the second screen/desktop. If there is a misconfiguration, you may not be able to access such an area.
You may also want to do a routine check for system file corruption, though unlikely, by using this method:
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The likelihood of this being a system file corruption problem is small, however. There may be a registry error or general misconfiguration causing the issue.
I suggest trying to remember when this problem started in order for you to perform a System Restore (Start -> Search -> System Restore) and try resetting the operating system back to before these incidents began to start.
A common problem may simply be that your resolution is out of range on the monitor and needs to be adjusted, as well.
