My car is crazy...AHHHHHH!!! The R.P.M gauge on my car is acting up.?

Up until yesterday the gauge was doing fine. Now, I cant go over 25mph and when it hits 25mph, theres a humming sound from the car and its just dragging. Also, while its doing this the gauge is close to three. Wow!! Why could this be?? Please help.....The car is a 95 Mercury Sable if that means anything. Thank you guys.