LEAK detection is a major problem. The leak line you get when using Hammer to load the pointfile in the 2D views will not really let you see what is going on (Red lines everywhere) If you are using Hammer 3.5 , then you might have a chance by following the line until it goes red, but it is not an exact science, and doesn't always point the LEAK out.
If you manage to get a .bsp then try typing 'pointfile' at the command line. You should get a single dotted line, follow that, and it might pass through the place where the LEAK is and then again, if the leak is big, it will probably run out before it get's there.
Compile often is the motto here... and as atom says, go back to what you just did and start there.