Found this by google:
http://support.microsoft.com/kb/125749/en-us?wa=wsignin1.0
Try resetting the prefs by reading this: May help may not but it is a easy fix. You have to time it right though.
http://forums.adobe.com/thread/375776?tstart=0
To me it sounds like something in photoshop became corrupt. In the software itself or the registry entries somewhere? Hard to say. Best bet, as already mentioned, is to reinstall PS CS5. Make sure you deactivate the software (if you can?).
Before you do remove the software go to start, search programs and files, and type in cmd. Righty click on cmd.exe and choose run as admin. A black looking box will show up. Type in sfc /scannow and hit enter. This will scan your OS files for errors and attempt to fix them. Have your windows 7 disk ready incase it asks for it. Also you may need to reboot to fix something. If you do reboot make sure once the computer is started and stable, do the command again until it comes up good with no errors.
Also run a virus scan in the safe mode to ensure nothing has infected your machine. Also to be a little bit more sure: While in the the safe mode type in MRT and hit enter. This is a microsoft tool to detect and remove viruses. Just run a quick scan. If something is found and removed then do a full scan afterwards.
Now PS CS5 might have a repair option on it when you put the disk in. Choose that first and see if that fixes the problem. If not then deactivate, remove, run the PS CS5 cleaner from the adobe web page, and reinstall. Make sure you run the software as admin. Don't install, explore the disk and look in the PS folder. Look for the .exe file, right click on that and choose run as admin. This will ensure the proper security levels.
Make sure you turn off any anti-virus software first. Turn off Windows defender if installed and running
