If the cables are stuck they are probably wedged in the winding mechanism by the motor, which are two pulleys connected with a spring to provide the cable tension. Once the cables lose tension, they can come off the pulleys and get wedged between the pulley and housing. I suppose could be a stuck motor or gearbox problem also, but I've dealt with cable issues myself.
I have worked on a couple of these now, if your cables are still good you can remove the whole motor/pulley/cable assembly from the vehicle, then take it apart and fix the cables. This is not an easy job, there are a lot of parts in that unit to make sure go back together properly but it can be done. In my experience you can't find people to work on these, they just want to replace the entire unit, at ~$500+ from the factory or $150-250 from junkyard. So if you tear into it and can't fix it, you are stuck buying a new one anyway.
If you decide to try it, there are 6 or 8 screws to remove the plastic cover, you can then see the cables wound around the pulleys and may be able to see your problem. To go deeper which you have to do if you need to fix or re-wind the cables, remove the 10mm nut which holds the pulleys, magnet, spring, and metal plate in place. Pay close attention to how this comes apart. The two pulleys have a spring connecting them together to provide the cable tension when they are pulled opposite directions. There is another small spring between the pulleys that flips a lever to provide a positive stop so the pulleys can't spin too far.
Once you re-wind the cables, you have to make sure you have the correct number of winds on the pulley to give the correct length of cable to wrap around and connect to the door pulley. ***Now the important part that took me several attempts to figure out!! Once you have the cables installed, you have to hold tension on them! If you don't, the pulleys will wind backward too far and flip the small latch on the positive stop that is located in between the pulleys, you won't know this happens but after the door runs once you lose cable tension. Then you get to remove the whole unit from the van and start over. The trick here is that there is a small hole in the middle of the pulleys that also lines up with a whole through the plastic enclosure. You can wrap the cables on the pulleys to have a little tension then slip a pin or strong wire through the holes to hold the pulleys in place. Once you have assembled the unit, then installed in the vehicle, you can have someone hold tension on both cables then pull the pin as you are connecting the cables to the door roller. Main thing to remember is don't let the pulleys wind themselves backwards.
If you need parts other than cables let me know, I believe I have a good unit minus the cables, so good motor, gearbox, pulleys, etc. Might even have control module. Would sell them at a reasonable used price if someone could use them. Don't recall if it is driver or passenger side but can find out if interested.