The voltage regulator is inside the Engine Computer and rarely fails. Sounds like either the alternator or the battery has failed. Unless the jumper cables were connected wrong, it is very unlikely jump-starting another car caused the problem, however, if there was a problem that was about to develop anyway, jump-starting could make that problem show up sooner.
Start by measuring the battery voltage with an inexpensive digital voltmeter. It should be 12.6 volts. If it's around 12.2 volts it is good but discharged. Use a battery charger to recharge the battery at a slow rate for an hour, then the voltage should be 12.6 volts.
If you find closer to 11 volts, the battery has a shorted cell and must be replaced. You can't cause that to happen. It's just a fact of life when they get old.
Once the engine is running, measure the battery voltage again. It must be between 13.75 and 14.75 volts. If it is low, we have to talk about diagnosing the charging system.
Wednesday, October 31st, 2012 AT 10:53 PM