GrandCherokee2000

I have a 2000 Grand Cherokee (Inline 6 cyl). A short time ago, some of the gauges began switching wildly back and forth, and most of the dash lights would come on and flicker, just after I started the vehicle. Most often this would stop after less than one minute and the gauges returned to normal.
This morning, I got in the car and it would not start (starter did not turn over-nothing), except that the gauges started swinging back and forth again, this time with the vehicle not started. I jump-started the vehicle (it started right up) and drove the vehicle for about 20 min. All during this time, the gauges swung wildly (although I did notice the fuel, temperature and tach did seem to be working properly); however, most of the dash lights flickered the whole time. When I returned home, I turned the vehicle off and attempted to restart-NOTHING. I noticed when I turned off the ignition, I could here a muffled, high-pitched ticking sound and, with the ignition off, the gauges continued to swing wildly. The high-pitched ticking I heard when I turned off the ignition stopped whenever I applied the and held the brakes.
PLEASE let me know what you think may be going on with my Jeep.
Thank you!