It is most probable you have a nastie on your computer,
Reboot into safe mode does SAS run then if yes do a full scan,
Reboot into SAFE MODE
1/Click Start and then click Turn Off Computer.
2/In the Turn Off Windows dialog box, click Restart, and then click OK.
3/As your computer restarts but before Windows launches, press F8 repeatedly.
4/Use the arrow keys to highlight Safe Mode, and then press ENTER.
5/If you have a dual-boot or multiple-boot system, choose the installation that you need to access using the arrow keys, and then press ENTER.
Note: If Windows launches before you can choose a safe mode, restart your computer and try again
PS/ Sometimes it maybe the F5 key