For several months now I have been using Hyper-V (2008 R2) to host a Win 7 VM. For most of that time I was able to RDP into it, recently I have not been able to. I am not aware of having changed anything, but it has stopped working. Any suggestions?
You need to know where in the stack you're looking for problems. If you're sure that all of the basic network settings are correct and verified that other network connectivity is working, check the firewall settings first, then run a WireShark dump on port 3389 as you make connections to the box to make sure that RDP traffic is actually making it over to the machine. Once you've verified that, you can start looking into issues in Remote Desktop Services (make sure Remote Desktop access is still enabled!).