Grinding gearbox..... Please help!

Yesterday my 2004 RR HSE failed to get in gear. I stopped at a store and came back, started it up and put it in drive only to hear a loud grinding niose. I quickly put it in park and then tried it in reverse and same thing. I was on a very slight incline and while in park it would not hold unless I had hand brake up. I had to tow it home and now don't know what to do. Please help!!

Thanks,
Spin718