I have one cat that just will not go in the litter box. I have tried everything I know to do. The other two do just fine. Is there something else I can try.

Have you had that one kitty to the vet? Sometimes if they get a UTI they go in places they're not supposed to.

Knowing some of this kitty's history might help to see what causes this problem. How long have you had him? Did you get him as an adult or kitten? Has he always been this way?

I too would recommend taking him to the vet as it could be a symptom of some pre-existing condition. You may also try getting him his own cat box as I have one that refuses to share his litter box and will potty in the tub if the other cats use her box.

Could be the litter. Have you tried to change the litter to see if the cat likes a new kind. I would take the cat to the vet also. Maybe they can tell you something- If all else fails- put the litter box under the bed??