Mk 3 GTi - gearbox problem

Any advice would be appreciated

I have a Mk 3 GTi and I have just lost 5th gear. My head is telling me that if the gearbox was shot then I wouldn't just lose 1 of the gears. Sadly I am not mechanically minded nor am I in the position to afford either a new gearbox or worse a new car. What could cause me to lose a gear?

Thanks in advance

i have heard that on them modles ther is a small gear inside used to change gears or sumthing like that and if it is damaged it can miss gears thus not allowing you to get into 5th gear there not that expensive either