For free virus protection, try downloading and installing AVG anti virus. It's a great, free antivirus program, and can be found here:
http://www.grisoft.com/us/us_index.php
Also, definately install AdAware, as it can detect spyware, adware, and some trojan's, and is an extremely useful tool to have on the computer. You'd be suprised to see how much crud you may have inadvertantly installed, and some of the stuff out there can really goof up your system.
Adaware can be found and downloaded here:
http://download.com.com/3000-2144-10...ml?tag=lst-0-2
If your system shuts down every time you run a game, or any program, it could also be either a heat related issue, a bad memory stick, or goofed up system files. I'm going to lean towards the second of the three right now, though, and suggest you run memtest86, which can be found here:
http://www.memtest86.com/
And if Nvidia discontinued the 4400's because of technical issues with the cards, I'm sure it would have been plastered all over the internet. I don't remember seeing a story along those lines, though. I know Gainward had issues with their 4200's, but not with the 4400's. If the 4400 is discontinued now, it's because of the whole FX series card release, and not because of problems with the cards themselves.