Have you checked the fluid level? If yes, depending on the mileage, you may want to get a transmission flush. this will include removing all the fluid( and is also the only way to get the fliud out of the torqe converter), a new filter and fresh fluid. But it could also mean you have a more serious problem. A flush can run from $150 to $200 and if it doesn't work most shops will generaly put some or all of that cost toward the prie of a rebuild or anoher transmission.

