clutch, gears, Rover 214I?

I have a rover 214I, bubble shape, and we have had a new clutch fitted,second hand gear box,new clutch cabel,this was done about 3 to 4 weeks ago, just lately i have been having trouble finding the gears, and now i carnt get the gears at all with the engine running, when the engine is off i can get the gears, as anyone any ideas, the car has about 90.000 on the clock N reg, befor I had the gear trouble the car some times judderd at low revs and we thought this was the gear box mounting,so we fitted a second hand one, and this sort of did the trick for a while,
the car has just passed its mot,
many thanks, dose any one want to buy it???
Allan