I have a problem with my Windows 7 Homegroup, between two Windows 7 Home Premium machines.

On one machine I get this:

The other machine in the Homegroup is perfectly happy and is able to see and browse this faulty machine as if there is nothing wrong. The Network and Sharing Center shows that I am joined to a Homegroup on my "Home" network and nothing is out of the ordinary.

I have tried leaving the Homegroup and rejoining/recreating it several times and that does nothing at all. Normal browsing to machine names and looking through folders seems to work, but it's a much more clunky way to get stuff compared to the convenience of the Homegroup facilities.

Starting the troubleshooter detects some problems with a "Peer Networking" (PNRpr or something like that) service not starting but fails to fix anything. Sure enough when I go to view the services via Control Panel -> Administrative Tools -> Services I see that both the "Peer Name Resolution Protocol" and "Peer Networking Grouping" services are stopped.

Attempting to start the "Peer Networking Grouping" gives an error that a dependency service will not start, the only service it is dependant on is the "Peer Name Resolution Protocol" so I try to start that and I get an error saying that the "service could not start due to error 0x80630801"

This has happened before and I have fixed it then by using System Restore and restoring the machine to a week before when I knew it had all worked. This time though I cannot remember when I last used the Homegroup from this machine and I've installed quite a bit so I don't want to go fumbling through restore points trying to find one that works...

Can anyone tell me if there is a way to reset things so that this machine is able to use the Homegroup again?