It could be the alternator, or the battery fried, or some other electrical problem or major drain elsewhere. Start with the battery, connections, and alternator. The battery seems suspect because it drained out all at once, while the alternator would've usually caused some intstrument warning lights to show up before it died altogether. The battery should have had significant power to run the car with warning lights on, before the thing died out on you.

The antilock/SRS light introduction to the problem is classic low voltage. Check the battery and check the alternator output, if you can get the thing running. If the alt is putting out 13 or so volts, it's likely not the problem. If it is low on output, you probably have a bad alternator.

--
chris herbst, five volvos.