Looks like Loctronics is out of business. I found this reference for you- http://en.allexperts.com/q/Car-Alarms-1513/2010/2/broken-prolock-alarm.htm that may help to remove your system.
The alternative is to buy the installation instructions for your specific version of the system and reverse the order to remove it. These guys sell the manuals- http://www.aboutsecurityconcepts.com/Loctronics_Auto_Security_s/71.htm