Okay so my c280 doesn't have an alarm equipped.
It already had a vacuum leak, so the drivers side lock wouldn't unlock with the switch.. works fine from the outside though.. for some reason the door unlocks from the drivers side (from the outside) but now it won't lock (from the outside) the key just gets stuck and won't move... any ideas?

 

try using the spare key. with my car, one of the keys doesn't like to lock the trunk (it doesn't turn all the time, just sometimes), but the other key does it fine. you can always try squirting some graphite into the lock and see if that helps loosen things up.

 

If it hasn't been used for years due to the fact you have a remote, the lock is probably needing lubrication and/or cleaning out of gunk. You might blast a short shot of Tri-Flow and then work the key in/out plus turn it a number of times.

 

used wd40, first i thought it was stuck, then i stuck a q-tip in there, did some in and out motions, more wd40.. worked.. thanks alot xvvvz