My 2001 hyundai tiburon has no reverse or overdrive?

i had cruise set & tapped the breaks to slow down a bit & when i put my foot back on the gas i heard a loud pop & the car just revved. i pulled over & called someone to come look at it. when they got there they got in the car & said it has no reverse or overdrive & its hard to shift into gears. it is an automatic. we got it back to my house but now we dont know if its the whole thats bad or something else. they said it does shift into second but it shifts really hard & jerks when it does & they cant go over 45. a friend of mine said it might be a bad solenoid but were not sure & i really dont have the extra cash to take it to a shop. how do we check to see if its just a solenoid & is it easier to replace that part or just buy a whole new ? any suggestions?