Fluorescent Bulb Inspection

My kitchen fluorescent light fixture has stopped working. How can I make it work again?

There are three light bulbs in the fixture with two ballasts (a small one for the center bulb and a large one for two bulbs on each side - both do not use starters). Before the fixture stopped working, one of the side light bulbs stopped lighting and when I replaced the bulb with a new one it didn't light. Rotating the bulbs didn't work either. I checked the ballasts with a multimeter and they seem to be fine (no resistance). I can't figure out how to open the tombstones to check the connections, but they seem okay from a visual inspection on the outside. The wiring to the ballasts and from the ballasts to the tombstones look good.

Any ideas of what is wrong or what to check next would be appreciated.

Thanks.