What should I do to fix my computer, the screen is black and it's reading an error message?

My computer is reading an error saying that Windows security Center has detected spyware/adware infection and it recommends that I use special antispyware tools to prevent data loss. I don't know what to do. I have Norton so I thought things like this would be prevented and on top of everything else it is now sooooo very slow! What should I do? I don't really trust letting anyone fix on my computer since this all happened a couple of months after I had it fixed for another infection that caused nasty pop ups!

What should I do to fix my computer, the screen is black and it's reading an error message?adware

If your PC used to be faster, or is acting strangely, it's probably infected with malware. Use the link below to learn more about "malware".

Then, you need to install: ONE Anti-virus (I use AVG free), ONE Firewall (Zone Alarm free), and Anti-spyware tools like: Windows Defender, Spybot, Ad-Aware, Spyware Blaster and cCleaner (free, use all 5 regularly).

Google for them, install them and learn how to use them (use Help TAB).

TIP: Last resort, back up (copy to CD / DVD / external hard drive) all personal data and do a Windows "Clean Install", get more info at (www.theeldergeek.com). The apps above can only clean up so much.

What should I do to fix my computer, the screen is black and it's reading an error message?antivirus scan