Steam... breaking on Mac

Something weird has been happening the last couple of weeks; my Steam package has suddenly been “dying”. The icon on the dock just turns into a piece of paper and compass, as if the computer didn’t know what the program was. This just happened again with ‘Steam 2’ which i reinstalled when Steam ‘1’ stopped working, when i simply closed Steam right now. Closed it and then the icon changed to the paper and compass, and now will no longer open.

Any ideas?