Dimension 2350, window XP

When I go into, control panel>user accounts as soon as I click on change way users log on and off a McAfee/Virus Scan  box pops up saying (A Suspicious Script has been detected) sript details are the following.

File: mshta.exe

Activity: the script is attempting to call the RegRead method within the IWshSell3 object.

File path: mshta.exe

Since the unit was new this spring I have had the welcome page as the sign on, yesterday that was gone and the logon windows box was there, so I tried to change back and discovered the script thing, I am not able to change back to the Welcome sign on screen.

Also I am not able to open the (set program access and defalts) or the (add and remove programs and windows components).

McAfee Tech told me to down load thew hot fix for article Q812400 and Q812960, MS sent me the link to 12960, I down loaded and the same problem exists, MS said 12400 is not available.

Any ideas, Thanks this is my first post.