Q: How to get to the main menu from home share

My first option would be to reboot the apple tv. if this does not work then you can do a restore.

If you have apple tv 2nd or 3rd gen follow these instructions:

http://support.apple.com/kb/HT3180

If you have the 1st gen follow these (you probably have 2nd or 3rd. not sure home sharing is part of 1st. only computer linking)

http://support.apple.com/kb/HT3199

I hope this helps.