Like sealbeach740 stated, double check the battery/charge. The liquid-cooled alternator should provide 13.2-14.5 V of charge. Also the amperage of the battery should be checked. The reason for your "disco lights" on the dashboard might be insufficient power supply to modules like transmission, ABS/brake, or even the DME. I would suspect a wiring harness issue also , a fault ground cable for instance.
JOY = BMW