When you say he "checked the ground," where is the ground? I have a ground at every light. I hate, just HATE messing around with grounds.
Easier in the long run just to re-wire it. If you just fix-it-up without knowing what actually caused the problem you will be right back here again 15 - 30 days from now. Or maybe 45... or whenever. When wiring is messed, a re-do is the best fix.
Tip: when rewiring, use all stainless screws and washers for your lights and grounds, leave extra wire behind the lights (about 6 - 8"), just loop it tightly and tighten with a plastic tie.