Transmission problem

[Akaiso]

Pls help n gimme solutions asap. My Volvo s80 once I start it, d P on d dash shows n once I move it coming to 3rd gear it drags n makes a jerky sound n at that point, d dash display instead of show P, or D, it shows a -, Dats a minus sign n den immediately, d car starts crawling like a car whose clutch is burnt. Then wen I off n start, d P comes on fine but once I move it jerks cum clunck harshly n d minus sign comes on n crawling sets it.
Took it for diagnosis n read Transmission speed line missing..... Whatever that means. Some mechanics suggested its d fibers gone, some say I shud buy another gearbox, some say its d Throttle Board. Av changed gear oil still d same story. Pls wat do I do? Its a 5cylinder, front wheel drive 03 Volvo s80, with dutch text display.