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Do you happen to have the Windows Firewall active on the laptop and/or desktop? I would suggest that you turn that off while you're attempting to network these machines.
Do both machines belong to the same workgroup? How are you connecting the machines? Do you have a router or switch?
Can you see the disk in Disk Management? It's possible you need to allocate the "missing" partition a drive letter for it to become available.
I need to know if my laptop hard drive has a security toggle that needs to be triggered before another computer can see its contents. I think
Did you have permissions or security set on the OS partition when it was in your laptop? Did you encrypt the folders of the drive?