If the shower head is clogged (even if it it is not I would still do this) remove the head and soak in coke (yes, it works), CLR, vinegar or bleach and see if you can dissolve the debris. If that is not the culprit, check to see if there is access to a shut-off valve behind or below the shower. It will be inside of the wall and is only acessable through a hole in the wall.
If that is not the case, it is now time to consider replacing the shower body. This is an involved job but something very doable by a competent homeowner.
Answers & Comments
If the shower head is clogged (even if it it is not I would still do this)
remove the head and soak in coke (yes, it works), CLR, vinegar or bleach and see if you can dissolve the debris. If that is not the culprit, check to see if there is access to a shut-off valve behind or below the shower. It will be inside of the wall and is only acessable through a hole in the wall.
If that is not the case, it is now time to consider replacing the shower body. This is an involved job but something very doable by a competent homeowner.
Hope this helped.