car wont start on 2002 Chevrolet Tahoe

Just stopped to get gas in a friends tahoe. Pumped
$10.00 dollars got back in and when i turned the key some sort of alarm went off and the car will turn over but will not start

Asked by for the 2002 Chevrolet Tahoe
a friends car?? sounds like a alarm issue. you either need a fob to disarm or maybe another key

thanks. he tells me that there was no security system in the truck. However there is an horn under the hood that i recognize to be associated with an alarm. Is there some way the key i have might have become unprogrammed or something?
you could try this. disconnect the negative battery cable. turn the ignition to the on position then reconnect the cable with the key in the on position. that should disarm whatever aftermarket alarm is there. then try to start it.