Hi Lisa,
Yup. Seen this before. I would suggest that you backup any Personal Information to external media from this computer if you haven't already done so. Then proceed to reinstall from your Recovery Disc or Recovery Partition to reinstall your win7 enterprise 64bit. Then re-enter the original Computer name you had originally; e.g.: JACK-PC, or JILL-PC, or similar. Reboot your computer and it should then rejoing the correct Workgroup or Homegroup (see detail below for further explanation).
This should reset all your permissions. However, Windows7 Homegroups are very quirky, so if your have one or more ADDITIONAL WINDOWS7 computers on your home network, you will need to take additional steps. Basically, you have to identify the FIRST Win7 computer *desktop or laptop* that got installed in your home network. Physically go to that computer and go into Homegroups and print or write down the Homegroup password for your home network. On the newly reinstalled Win7 enterprise 64bit computer, go to "JOIN A HOMEGROUP", and enter the Homegroup password you pulled off of the first win7 computer installed in your network. If you have any other non-Win7 computers on your home network such as XP or Vista, this shouldn't be required.
Also, if this doesn't fix it, and you write back for more help, please provide the EXACT Make/Model of the Computer you are having this difficulty with. If you need more detailed step-by-step, write back and I'll try to provide you some links.
Best of luck to you,
<<<BIGBEARJEDI>>>