After the shower walls of sistine stone were grouted to the cement wall board it did not hold and came apart what could have happened ?

Depending on how hard the grout has set, I would use a small, sharp Cold Chisel and small 2 Ounce hammer, to very gently chip away from the tile surface toward the grout joint.
Be very careful not to damage the tile surface.
Then finish off with some 000 wire wool to polish the tile.

epoxy grout by mapei will work.

problem usually happens when grout is not fully cured and sealed when water penetrates it so... remove old grout using grout removal tool (you can pick up from any where that sells flooring(tile) pick up some new sanded grout to match and sealer apply then seal 24 hrs cure time is req. before sealer wait 2 hrs then re-apply sealer

The grout between tiles is just for filling the gaps. The tiles are glued to the wall, usually with "thin-set" mortar. Unless that mortar is in very poor condition it is unlikely that you would be able to remove that single tile without breaking it. The wall behind the tile might be water-resistant drywall (a poor quality situation) or it should be cement-board. I suppose it's possible that there is already a hole in the wall behind the tile, but the hole would be smaller than the tile, and assuming 4 inch (not large) tiles, this is a poor choice to gain access to the pipes. The usual access is through the wall from the other side. During initial construction, a removable access panel is sometimes provided (depending on local building codes and whims of the builder). If there is no access panel, and the other side of the wall is drywall, then cutting a generous hole, and fashioning a plywood panel (with trim around the edge to cover the gap between the drywall and the plywood) is a pretty standard and simple approach (depending on your skills). As an alternative and for more info, here's a link describing how to install a plastic snap-in access panel. Good luck! http://www.diylife.com/2008/06/23/plumbing-access-panel-installation/

There are two ways that I would do it depending on the width of the ledge on top of shower base. If you have enouch room I would shim studs with strips of material thick enough to bring the surface out even with flange on shower base. Then I would put cement board(wonder board) on wall and over shower flange to set on top of shower base. Finish seams on wall board per manufacturers directions,Let seam filler dry then seal with thompsons water seal or equivalent sealer. Let that dry then tile on that grouting and sealing with quality caulk at joint between shower base and tile.
If ledge on shower base is not wide enough then I would place cement board directly to studs then use filler strips on face of shower base flange to bring two surfaces flush. Water seal let dry and tile again coming down over top of shower. Grout and caulk to finish. P.S. I would use a siliconized latex emulsifier to mix in with grout. It gives a better ware proof seal. Hope this helps you. Good luck and thank you.

You will need a chisel and a hammer for this. Will have to cover bath tup, shower base, anything that may chip from the fallen tile pieces. Start hammering the chisel behind the top tile, or smash the corner of a tile and try to remove it to be able to start. Be careful not to brake the plaster, this is the biggest problem when removing wall tiles. Keep hammer the chisel, and remove bit by bit all the tiles. Patch with plaster if big areas will get damaged in the wall.

Let it all dry. Then just buff it off.

liquid nails will do the job but you can also use clear silicone provided both surfaces are dry.

this may not be a grout problem . I want you to run the shower and check the shower arm behind the wall plate and the toe tester(spout ) for water leaking behind the wall.If you dont find a leak than their could be a problem with the rubber membrane under your tiles.