OK, here's a two methods to fix this problem.
Method 1: The Long cut!
1. Launch Windows Task Manager. (by pressing Ctrl+Alt+Del keys)
2. Locate the process “WgaTray.exe” and press end task.
3. then restart your pc and Log-in into the Safe Mode by Press F8 before windows boots) and delete the file WgaTray.exe from c:\Windows\System32
4. Delete also WgaTray.exe from c:\Windows\System32\dllcache
5. then Type regedit in Run (Win+R) to open Registry Editor, navigate to
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Notify key6. then Delete the folder WgaLogon and all of its contents.
7. After that Restart the PC normally. and Its done!
Method 2: The shortcut
Just download and run RemoveWGA.exe
and its done!