Alarm won't shut off (W126)

Benzoids ,

I can't get the factory alarm to shut off on my 91 560SEL!

The car was sitting for about 3 weeks, I unlocked the driver's door, started the motor (no probs there) and it sounded.

Shut the car off, shut the door and lock/unlocked per the owner's manual.

Now, in this case it didn't stop. First I disconnected the battery, thought that would re-set it, but didn't -- bad me!
So I pulled the fuse for central locking, power antenna etc. That's where I am know.

The deal is that it has an after market Viper alarm. It was not "ON" when the car was in storage and has yet to give me probs.

I spoke to a MB mechanic and he seemed to think it was the outfit that put the alarm in.

Oh yeah and also my radio is asking for the code (to which I dont have!) Ugh... any ideas on this one?

Thanks in advance!