how can I fix my problem?

cables are bad for seizing on these,also if you remove the air filter,battery,battery box,engine mount to gain access to g/box,remove the ring of 10mm bolts and lift the lid off the g/box,there is a roll pin on the selector shaft which shears causing loss of gears,maybe wortha look also,you can `t get these roll pins from Ford now and you have to take the whole selector unit which is very expensive,a scrappy may be worth a go.If all is well otherwise then it sounds like a g/box fault. If it goes into reverse ok with the engine off then I would suspect the clutch is at fault, but would expect 1st gear to be tricky also.

cdc
October 2013