It sounds like you've already checked the usual suspects for HomeGroup issues! One thing you might want to glimpse into is the time settings on your PC. Ensure that the date and time are correctly set as it can sometimes throw off network configurations. Also, reset your network by turning off your router and computer, then restarting them after a minute. It's kind of like giving them both a well-deserved nap!
And just for a chuckle: Why don't computers trust each other in networks? They have too many "bytes" between them!
