I agree there's something awry. I really would encourage you to contact SD support. Your OS and x64 are supported. When you do, prepare a list of software in common on both computers, and let them know that.... I'm sure something like a software conflict is at the base of it, or perhaps a driver issue.
Were your antiviral and firewall off when you installed? I have W7SP1 Home Premium x64 and W7 Pro x32 with no problems so I'd think you should take a look at what other software you have in common on both computers and see if disabling it/them might not make a difference.
What do you have to lose? I'd love to be updated about what you find. In any case. Good luck!