My track lighting is not working, but other lights on the switch are. Help?

I have a track light system that has 5 halogen bulbs that hang from a cable. Two cables stretch across the ceiling about 12 feet from a junction box. on either side of the track light system are can lights. They are on a 4 way switch. They have worked with no problems for years, and for some reason one day, none of the track lights worked. The cans still work fine, but for some reason not the track system. I tried replacing a bulb, but that didn't help. I used one of those cheap electricity sensors that you check the power at an outlet or switch and put it on the cables, and it beeped as if there is power going down the line. It did the same at the bottom of the cables where the bulb fixture is attached. What gives?! Any ideas? Thanks