And did you try SAFE MODE?
Windows Vista Home Premium SP2 Dell Inspiron 6400 laptop
I recently received the following message "Couldn't start the Security Essentials service: The specified service does not exist as an installed service".
I ran "rkill" and then ran Malwarebytes Anti Malware. Then I ran Superantispyware.
I then downloaded and installed Avast. I noticed that Avast gave me 2 alerts (program blocked 2 threats). Avast required me to reboot computer to complete installation.
Once I restarted laptop, I cannot type in password and the arrow cursor won't move at the main screen.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic