how can i fix my alarm?

if one works the other don't even with new battery its obiously faulty.

Or, only a guess, if you have to set fobs to operate alarm when first installed then try re-setting the offending fob.
like the radio when vehicle battery removed, you have to enter code to re-activate the radio. In case of alarm it may be by pointing fob at alarm and press buttons to activate/link to alarm

bb
February 2011