I changed the baterry on my previously running cherokee and now wont even turn over

no need to adjust the timing you need to turn the rotor to the left a it will start and it's not a v6 jeep only make inline6

is the battery and the conections good? not croided. have you check maybe you need new spark plugs and wires or possible fuel filter may be pluged and engine is not getting enough fuel, may need a change

the starter sounds like ur problem for starting the jeep since u changed the battery the computer really did not have to be changed and for the car only running for a couple hrs u might have a clog in ur fuel filter located by the gas tank under the car very easy to change once u locate it. it doe not sound like ur fuel pump cause the car does run for a couple of hours if it was the fuel pump problem it would not even run for more then 10 mins if that.

your blower motor relay is probably stuck on. It is normaly under the hood in the black fuse box. If you tap on the top of it it will probably shut off. If it does this just change that relay i think they are about $20 at the dealer.

idle air control valve, maybe.

Check for fuseable link in main power cable.

check the IACsensor it may be sticking

Check the condition of the heavy cable running from the battery to the starter solenoid on the starter.

change thermastat check starter wires if tight change starter

Sounds like you activated the factory alarm.
Hook up the baterry and unlock the drivers door with the key in the door cylinder.