Stability problem (_stdcall on win2000?)

I have a small 3D engine for a mini game, but when I make to many calls in a small amount of time, the program crashes. It either tells me that the BOOL done doesn''t exist (variable used to check if it is the end of the application in the mainwin function, or it tells me that ESP wasn''t kept and it is a calling convention problem. I read that win 2000 had compatibility issues and that we should always use _stdcall instead of c_cdec. I set that option in my compiler, but it still crashes... HEEELLLLPPPPp Thanks.