Do you have Admin Privilages? If you do, try reinstalling Plus! Again....
If that for whatever reason doesnt work, you have some sort of Malware on your computer
I recommend BitDefender(Get the 2008 trial then scan computer, then uninstall it and download the Bitdefender 10(free edition) for Anti-Virus, and Super Antispyware(free).
Or PM me for the full 2008.....