To even begin helping you I would need to know whether it's an automatic or a manual, and know exactly what it's doing (skipping, making noise, not going into gear, etc.) Take it to your dealership, they'll help you out.
Take it to a shop for the tranny. The shop will have to take the sealing around the housing outside apart or put on machine to trouble shoot the problem.
For a tranny you have to take it into the shop and have them do it because it is a sealed housing around the outside of it, They will be able to either take it aart and tell you what wrong or they have a machine that will trouble shoot it for them.
