Windows 7 "Previous versions are not available"

[snalmond]

On my desk top PC running Windows 7 Home Premium 64 bit, I checked the properties of various files and folders and found that "previous versions are not available." I checked properties of files and folders on a netbook running Windows 7 Home premium 32 bit and found previous versions are available for "Restore Previous Version" on it. I went to Control Panel>System and Security>System>System Protection and found the settings on both PCs to be identical. Also, each was configured to allow adequate space for storage of previous versions of files and folders. In each of the PCs, Volume Shadow Copy service was started. What else might I check and what more must I do to have access to previous versions of files and folders on the desk top PC?