Can't pull choke knob up on my riding lawn mower

possible bent damaged seized shaft, look under deck for excess debris, rope, damaged blades

It has small spring clips around the base of the pull knob end on the inside of the operator station that must be depressed to remove choke cable assembly

Check that the blade brake is disengaging. Slip belt off blade spindles and check that they spin freely. Check underside of deck for clogged grass, ropes, wire, etc.

sounds like a bad PTO, that is the electrical gizmo on the bottom of the engine's driveshaft which engages the bottom pulley, running the deck. you might luck out and find the fuse is blown so follow the wire from the PTO back until you find the fat part in the wire. the fat part is an in line fuse holder with a fuse in it. if the fuse is bad and blows again, you need a new PTO

what kind of mower is it?
For any mower you need to check that you have proper oil level, and that there is gas in the tank. If it is a riding mower there are a few things to know before you start. There are safety interlocks that have to be complied with before a start is permitted. The blades must not be engaged. Someone must be in the seat, and the brake must be fully engaged. Move the throttle to choke for starting (or pull the cable out if that be the case), start mower. Return choke to normal operating position.
For a push mower check your oil and fuel. Prime the carb. if necessary, push the button by the carb. until you are pushing fuel and then a couple more times. If it has a throttle cable put in choke position. Pull back on the safety bar. Pull cord to start. Throttle cable to normal running position, generally full throttle right before you start to engage the choke.

I hope this helps, if any questions just reply. Be sure you let me know what you did and what kind of machine it is.

If this is really helpful, please rate.

if it is already running and you "engage" the choke, you will flood the engine with too much gas and it will sputter and die. the only time you engage the choke is to start the engine when it is cold. if the mower dies when you remove jumper cables, and you leave the choke alone, you need to have someone look at your charging system.

Check throttle cable at carb and make sure you have full travel. Sounds like rpm is little to low. Throttle cables are usually held in place with 1 screw and a washer. Put cable at full throttle loosen screwand pull back until throttle at carb in at full then tighten screw.

You may have to replace the choke cable assembly. Sometimes they rust to outer sleeve

You deffinately have a loose wire or connection coming off that switch,youll have to investigate to find out where it is.

Belt may have come off. Check the wire from the clutch and from the switch, you may have had hungry rodents during off season storage.