2000 Honda Odyssey alarm problem

Hello, I have been have a lot of trouble trying to start my car. The previous owner installed an aftermarket security system of which I don't have the remote for. I have been trying to research what I can about it but have come out with very little results. Anyways I believe that the security system is keeping the starter from engaging when I turn the key, and I THINK that it's because the battery has been having trouble lately holding a full charge. I did read in your topics that some systems are designed to failsafe whe a change in battery charge, which makes sense. Anyways I am asking, what do I do? Is there some secret trick with that "valet button" under the dash? Or is it possible for me to just take the system out? Please help :(