What year is the car?
Had you have problems with getting into gear prior to the fault?
Any recent work done on the car?
Ok..the first obvious check would to check the shift controls to the gearbox it "possible" one of them may have popped off..normally these will be cable operated from the gearstick housing,unlike the older version with the solid bars...so you 'll need to get access or have look at the exterior selector mechanisim on the gearbox to ensure they are still attached..following that you can have someone in the car try going thorugh the gears like you would normally and see if the selector at the gearbox end responds - if not - then the problems likely at the gearstick end within the housing below the gearstick itself in which the other end of the selector cables attach or likely one of the cable has snapped..either way thats normally the first checks that need to be made here before moving on to anything else..I do hope this helps
Exterior selector mechaisim is what the other of the cables are attached to outside the gearbox. - but it should be standard checking you need to get access to the top of the gearbox and check they are still attached..the first step id say would be the gearstick end..pull the gaiter up then the section of plastic trim around the gearstick you can gently prise it off all the way round as its just clipped on..observe the arrows in example pic of interior on 2008 carens...and check the stick itself hasnt become detached..