Arduino Leonardo doesn't get auto-detected in Windows 7 (64bit)
Ok, step by step. Does windows make a sound as if it has found new hardware? Does anything pop up or Device Manager show a new device (COM1 is default for windows, not related to Arduino necessarily)? 

If not, then the Leonardo board isn't doing anything to be enumerated. This is likely a hardware issue. Try a different USB cable or test it to make sure it works well. Perhaps a jumper is missing or a solder bridge is missing (on Arduino uno there are two points in the back that need soldering). 

Did you follow the instructions Here in the communications section?