I have a prison which has beds and everything but prisoners won't come.…

I had the same problem at first. I'd have my prison set up and then nothing. You just have to wait, look at the sky and you will see a plane fly into the hanger, then a bus drive out the hanger and into your prison. Then a load of inmate will walk out and go into the dorm. The first 2-3 buses only have 203 inmates for you. Be careful, your money will run out fast with almost no income form the prison population.