harmonic balancer/ crank pulley

I went out wheelin this weekend and my jeep started overheating and not charging the battery out of the blue. so we strapped it back home and i got to looking into the problem and it appears as though the crank pulley is not turning the belt thereby causing the water pump not to turn and the same with the alternator. why would it do this? could the harmonic balancer be shot? how hard of a job is this to do in my own garage...

also how hard is it to replace a u-joint? my drivers side front is acting like it's gonna grenade next time i drive it...

tia

Yes they go bad,usally they walk apart,throwing/tearing belt or grinding into the timing cover.Not a difficult job,lots of stuff to move to find room,a dampner puller and replacing tool,and new belt is all that is "usually needed. Some will replace the crank seal,some will go on into the motor and change the timing chain/gears,depends on the miles and your mechanical ability.
U-joint ,biggest problem is removing the unit bearing without damage.Remove wheel,brake pads/caliper,rotor,unit bearing,and pull out axle.
Wayne

thanks man. it only has like 20-30000 on the motor... and im pretty mechanicaly inclined. ill probably do the crank seal and ill look at the gears and chain... first jeep so thats why im asking this stuff... all i've ever had is older BMW's and VW's and they are pretty easy (to me anyway) to work on...