PC virus infected - to install another HDD to scan.

My PC anti-virus is not working. Error message "Active
Shield is not properly install or some of component is
missing. Please reinstall it"

Even after I deleted and reinstall the McAfee anti-virus
the same error message appeared. The computer slow down
and most of the file/folder on desktop cannot be opened.
Can't do online virus scan either. Have tried various
ways, still cannot resolve it. Please help.

Can I purchase another Hard disk drive and install in the
PC as master and change the current HDD as slave to scan
for virus. If can, please advice how to do it.
Many thanks.