2002 Jeep Liberty had a alarm system now won't start say the alarm is active when it was not stopped for gas and now won't start because of the alarm how can I get it started again

It will need service
you only have one key?
this is called, and immobilizer.
if the key and antitheft system are not happy , they tall the engine brain (PCM) to be DISABLE, called immobilized.
it needs service.
the first step is check fuses.
then scan it,
the scan tool will tell you why.
for example it might say , wrong key code. (a bad key)