Now I am not sure what your trying to do, it sounds like as if your trying to use the 32 bit Home Premium key for the 64 bit professional. This is NOT possible, as each key is proprietary to the Windows 7 version it belongs to.
You need a 64 bit key, the bootable CD and do a clean install.
You can do this by booting off your disk. After installation of the 64 bit Professional you will be asked for a 64 bit Windows 7 professional KEY.