os scanning software

What is a good operating system scanning software to make sure everything is running right? sometimes the computer goes slow i ran adaware. i use it all the time. i cant seem to track down what is going on. right now i cant connect to the internet. when i try to get into my command prompt i get "the ntvdm cpu has encountered an illegal instruction. choose close to terminate the application."

Where can i start to track this down?

 

also, noticed my task manager won't come up when I do ctrl+alt+del.

I'm following instructions in this link: http://www.bullguard.com/forum/8/Another-CTRLALTDEL-issue-task-_24871.html

 

What is the operating system?

Do you have the Windows CD?

 

I have winxp and yes I have the cd

 

Start, run and type in sfc /scannow (there is a space after sfc )