The other guys here have some good approach. Here's mine. It's simple and could possibly work. It's tough troubleshooting PCs when you don't know the exact problem. Your blue screen leads me to believe bad RAM at first, but try memtest to test it out or other free utility if you can find them. See how that checks out. If it turns up fine and you've done all the other steps above, then try the simplest things.
Do a complete Temp Internet File cleanup, Cookies, History. You have a lot of movie files, music files, picts, etc? Get those off the hard drive by backing them up onto DVDs. This is tedious work, but you're going to have to do that eventually one of these days.
Uninstall all programs that you are not using or less likely to use. Uninstall the two games that you've been having problems with. Then reinstall them. Perhaps there's conflict with file sharing among the two. I'm thinking if it may be a video card problem, the entire screen will be affected, not just the games. Try getting rid of the drivers and just use plain Windows VGA crappy drivers first. After you got everything removed, run scandisk. Correct errors if any. Then run defrag if you wish. After all that, do a reboot to start out clean.
Now this is tedious and long work, but you got to take it step by step. See how Windows run after all that work. You should be running Windows basic VGA. Now attempt to download new drivers for your video card and install it. Probably ask you to reboot after that. Now make sure you have latest Direct X 9.0c on there. Install one game only and run it.
You may want to check what's in the Task Manager to see if there's anything out of the oridnary that you've never seen before. I check mine alll the time when my system halts or slow down. I just end the process to get rid of it, then it runs at full blast. Go to MSCONFIG to get rid of some startup items that you don't need.