I broke the transparency of my shelves

Could you give a bit more detail on what exactly you're going for with this in terms of its appearance? Is the whole thing meant to be glass? Are the horizontal shelves meant to be glass only? Right now this is what I see in S4S:



It appears you set the dropshadow mesh to glass, not your actual shelf. Dropshadow is that shadow rectangle/circle under the object.

Phongalpha will already work like glass if you add a degree of transparency via the alpha channel, so there's no need to change it to glass (unless you actually want to, glass shader tends to give a more vibrant glossy result).

The reason your shelf isn't behaving is because you didn't separate the meshgroups properly. If you want the frame and the side bits be solid, they should all be in 1 meshgroup, and horizontal shelves in the other.

Right now this is meshgroup1:



And this is meshgroup 2:



So you have the majority of the frame AND shelves as one group, and random side parts of both as the other. That would explain why you get no transparency on the shelves - meshgroup1's shader is set to phong.

You'd need to either re-separate the mesh (join the side bits with meshgroup1 and have shelves as meshgroup2), or you can leave the mesh as it is and change phong's shader to phongalpha.

On another note, if you're sticking to solid block colours for your texture, I would suggest significantly decreasing it in size. Right now something like over 70% of your UV map is empty, so it's a lot of wasted space on your 512x512 texture. You could actually get away with a VERY small texture since there is no detail/shading. That would decrease your file in size.