Well, I ended up not only resoldering a couple spots on this one. When I opened it up, I found that apparently, someone (not me, I know this for a fact) had spilled a bunch of soda into the machine. So I ended up soldering out all of the important stuff (like chips and stuff), washing off the board on the advice of a friend (ever so gently) with lukewarm water, and air-drying it out. Then I resoldered everything back. Voila!!! It works again. I took out the chips because I didn't know how they would respond to getting wet--better safe than sorry I figured. But it works now! Thanks for your help guys and gals!

BTW Zektor, I knew it didn't come from a dirty cart, because I am (self described) quite anal about keeping my carts clean, especially the contacts. Nothing gets stuck in my machine's slot unless it is disease free and checked by a physician. But thanks for the tip.