transmission won't go into drive or overdrive

I had this problem with my 2000 Sebring convertible JXI 6cyl along with no speedometer function. I'm sure you have resolved this by now but for other folks looking for answers this is what the solution was for me. Took the car to tranny shop. Mechanic put it on the computer. There was no signal coming from the OUTPUT SPEED SENSOR on the transmission. When this sensor goes the computer puts the car into LIMP mode (enough power to limp to the service shop). The part cost me less than 20.00 at AutoZone. With a little more research or advice from your parts store you'll find that it's an easy part to change. You'll need a 1" open end wrench to remove it. The nut is plastic and does not need a lot of torque when tightening.

Check the transmission oil level first but after that the problem is most likely in the transmission unfortunately.

Check the fuses under the hood I had a fuse blown and the car would not shift into overdrive...also is your speedometer working? If it is not this is most like the problem.