screwdriver

I've had this 21 speed Schwinn Aluminum Comp for about 3 years, and probably rode it 3 or 4 times. I was getting it ready to give to a neighbor kid whose parents can't afford a bike for him. I test rode it down the street and back, and while going through the gears, the front derailleur just came apart while I was shifting into the tall sprocket. Now I understand why nobody wants a Walmart bike. It's long out of warranty so I need to find a front derailleur. I also need some instructions on how the cable is ran and connected, this one looks weird. Any help?