The battery might be dead for good. You already know it ran down to dead as it wouldn't do anything when you tried to start it.
How old is the battery? What brand & size is it?
Being how it's that dead you'll want to let it trickle charge at least overnight, 24 hours would be better.
If I was you I might want to pour a little oil down the fill and down the filter canister as well before you try to start it.
Cosmos Black/Black 1995 540iA M-Sport
BMW Individual Exclusive Edition, 1 of 65 total, 9/25/95 Build