Just my observation , but a lot of malicious virus when they get into your computer they attack your Registry files in such a manner, as to make an entry in the registry, which at least at your next reboot, it(malicious virus) gets to run it’s own software and not allow the real windows software to start....
Now to correct this one has to get into the Registry file and delete this virus entry..
You have to be able to run (regedit) either at command prompt c:\....... regedit.exe OR
If you have a start button do Start-All Programs-accessories-run-(regedit)-Ok
Now navigate as follows and delete suspicious entries.. and than reboot..
the following is the way to see unwanted start up processes....deleting is simply right clicking on the item, and select delete option
Run regedit
and navigate down as shown
HKey-local-machine
Software
Microsoft
Windows
Current Version
Run
And / or
HKey-current-user
Software
Microsoft
Windows
Current Version
Run