Dead Battery now car won't Start

I got a 95 BMW 530i. My battery went dead due to sitting to long. I installed a new battery now it won't start. I need to know is it some kind of security feature or what. Any iodea would help.

Now that you've got the new battery in, is the motor turning over when you twist the key? You know, rrrr-rrrr-rrrr?
Have you got any evidence of juice at all?
If you do have juice, I suspect you've pulled another wire loose in the process of changing the battery.
If you have no juice, no lights, nothing at all, I'll bet I know exactly what the problem is...
More information, please, and I'll go out in the parking lot to look at my car to see if there's anything that would be easy to jar loose.
Back soon.
Flunky

No. It won't turn over or anything. Someone said it could have lost memory to the key whatever that means. if you know anything about this or anything else that might help please let me know.

If your car has NO signs of juice, that is, the lights don't come on, the starter won't turn, etc, it's usually because of a blown fusible link.
A fusible link is a wire that is small enough to burn through the moment the amps running through it get too high, for example when something shorts out.
The idea is that the fusible link (acts just like a fuse) will burn through in case there's a short, before the wire gets hot enough to catch on fire.
Find out where the fusible link is, and replace it. On Hondas, it is in a little box about a foot away from the battery, and the box says, "Fusible Link" on it.
They only cost a couple of bucks. Some cars have 3 or 4 of them.
Flunky
PS-And if the fusible link is indeed the problem, it means your old battery wasn't really dead...did you have it tested?

I just looked under the hood of my car. I couldn't find anything resembling a fusible link.
Time for me to get a manual!
Flunky