Holes in Aparment Basement Corners - Spring Flooding

I have a basement storage area in a 4-story apartment building that I converted into a gym, but every spring (or thaw) I get flooding in the basement.

Because the floor is permanently wet where the walls meet the floor along two walls, and there are even a few holes along one wall and the corner, I am assuming that this is where the water is coming in. (It is definitely not coming in through the one window.)

I have reported this to building maintenance, but there are on-going issues that have not been resolved with the builders and I am tired of waiting for the problem to be tackled properly from the outside. As they haggle I continue to get flooding and I cannot use the space as I want to. In addition, I currently live in the Czech Republic, which means that things are being resolved VERY SLOWLY.

So, although I understand what needs to be done has to be from the outside first, I can only control the inside - i.e. my storage space.

How can I "waterproof" or seal off the space?

HELP!!! SOS!!!!