Windows 7: can no longer share with networked pc..suspect windows firewall problm

Am using Windows 7 with 2 networked PC’s DESKTOP & LAPTOP
File sharing has previously worked okay but now Im encountering a problem
When trying to share files from my LAPTOP to my DESKTOP
When I open my Network and Sharing Center on my LAPTOP and click on the Homegroup icon
The DESKTOP & LAPTOP icons appear
When I click on the DESKTOP icon I get a window with the message
\\DESKTOP is not accessible, you might not have permission to use this network server
I thought it might be related to the Windows firewall settings on the DESKTOP PC and when I tried to open the Windows firewall I got an error message 0x80070724 indicating I cannot adjust the settings in Windows Firewall.
Thinking I may have a virus or a rootkit problem I ran several antivirus programs as well as Malawarebytes, and found no serious problems.
How do I fix this so I can access all the files on my DESKTOP PC???