Low tire pressure yellow light on-NEED HELP !!!

My 02 Impala  Police edition ,has "LOW TIRE PRESSURE" light on...I change all my tires and from that time I have this problem.I tryed to reset the light using my radio,but I dont have on radio display "TIRE MONITOR" thats not working,I tryed other way with ignition on and interior light set up for three time...its not working...How many psi must i  have  in the tires ??? And  is other way to make the light to go out...Please help !!!!!

are you making sure NOT to pull out the stalk all the way, rather to the middle setting (put car in on, pull from in to middle 3 times). Regards
Also some ppl claim if you discooenct the battery it will help, also the ar should not really be started when you do the stalk thing rather the key should be in the on position without the car actually on

on the older impalas tire pressure is not measured like on the new impalas.
the older- when a tire is at correct pressure, all tires are same size (diameter). so they all rotate at the same rate.
when a tire loses pressure, it gets smaller, the diameter decreased, and so a smaller tires will rotate MORE than a bigger tire over the same distance.
the ABS sensor detects that a smaller tire is rotating MORE than the rest and sets off an alarm.
may be wise to check out the ABS sensor

 
Thank you ,for help !!!!!!!
The light is off ,I disconnect the battery,and a push the brake for 20 seconds to reset the computer again.The car is working .
Thank you !!!!