Hyundai Accent Forum : “hard to change gears and has no reverse”

It could be a number of things, too many to list here. You will probably want to get it seen to by a mechanic.

Check the transmission cable to make sure it doesn't need to be adjusted or if it's worn. Check the transmission control module.

There really no quick fix for a problem like this.  If you have the dealership or a mechanic run an engine diagnostic check it will tell you exactly what is wrong.