Really sounds like it's not charging the battery. Missing ALT belt might cause such in an instant. If that's the case, you might loose the water pump, power steering, etc just as fast. Loss of water pump can cause further engine damage, so procede cautiously. I'd do a visual inspection while your have the battery charging with a battery charger. Then, if you have a volt meter, hold it on the battery posts of the battery. (Not the cable clamps.) Note voltage. If battery is good and charged, you will probably see 12-12.5 volts. Then have someone start the engine. (or do yourself) Then check the voltage on the posts again. I would expect to see 13.5-14.5 volts if it is charging the battery at all.
Guess this is just a start, please get back on what was found or tried and did or din't work.