Debugging while game is running

How can I debug my game while it is running? What I''m trying to do is in my Tetris clone, for some reason when you get a complete line and it is supposed to erase it, it doesn''t. So I''m trying to debug it and I play it until the point when the debugger is supposed to kick in, but when it does my game freezes and I have to end it with the old Alt+Ctrl+Delete and when I go into my code the debugger is up but once I try and go through my code the debugger greys out and I have to end it as well (obviously because I had to end my game and it is not running anymore). Is there a way around this problem? I know where the problem is in my code using error checking, but I don''t know why the problem is occuring. It is just a simple if statement that is not returning the correct value. Thnx in advance - Dan He who laughs, lasts