Transmission prob on a 1994 bonneville?

i was driving down side street. started to hear a ticking noise. then a deep loud thud. while driving it would go in and out of gear. now i do not have reverse, the gears are just grinding. i can increase the rpms and the grinding stops but i still have no reverse. i can put it in overdrive, drive, 2, 1 and the car will drive but it will go in and out of gear no grinding just seems like it goes to a neutral position. i want to fix it my self but i need some ideas where to start