Instruments fail and car won't start?

I have a Vauxhall Vectra 2003 model BB11. There is an intermittent fault. When driving along the battery light,ABS light and power steering light all come on and all the instruments stop registering. The car still drives normally. Sometimes the fault clears itself,but if you switch the engine off while the lights are showing the car will not turn over or start. After twenty minutes or so there is a click from the rear of the engine and everythingis back to normal. The car has spent five weeks at the garage and auto electricians without a cure. Nothing is registering on the computer diagnosis. HELP!!!