Entire dashboard goes on and off
You most likely have a connection on the back of the instrument panel that is either loose or corroded.
It is pretty easy to pull the instrument panel out. You could get a Chilton or Hayes manual at most auto parts stores for around $25.
You might just have to unplug and replug the connectors a couple of times.
This problem is not uncommon. A guy here in Duluth advertises in the newspaper that he will repair/rebuild GM instrument clusters.
Check to see if connector is tight in the back of the cluster if so then get it rebuilt or replaced .