Mega 2560 will not upload code

I am using a different computer other than my gaming system to test my Arduino code and every time I try to up load the code I get a error message saying that it has timed out or the com port that I am using is in use with another program and it is not. What can I do so that this computer will let me verify and upload code. I have tried both 1.0.6 and 1.6.5r5, neither will work. This computer is a 32 bitt system using windows 7 HP my gaming system is 64 bitt windows 7 hp and the code works well.