98 Pontiac Firebird alarm not working

Just this morning went to use remote to enter car, didn't work so I used key and now the system won't reset.  Bought a new battery, cleaned contacts - no good.  Stopped by dealership for assistance, they tried to reset valet button under dashboard.  Was short on time and money (wanted to charge $80 to disable).  Can a dumb blonde disable the annoying horn and just open the door by using the key?  Dealer surmized this was an after market installation.  Bought the car used and would have no clue as to type of system was installed.

Thank you in advance!

Thanks for the response.   I bought the battery for the remote and that still didn't work.  So I brought it inside to make sure I had battery in right way and noticed some dirt accumulated on the contacts.  Using a qtip from the office first aid kit and some rubbing alcohol to clean them, it worked like a charm when I left for work that day. 

I have no way of knowing the manufacturer of the system, can't find any markings on remote or under the hood.  Let's just say I won't be using the system anymore.  Plan to trade car in within next couple months, so it will be a SEP.  Someone else's problem.