Screen sharing stopped working after 10.10.2 update
After working with Apple, I have an answer. It looks like the 10.10.2 update changed your firewall settings. Try this:

System Preferences>Security and Privacy>Firewall Options

Scroll down the list till you find "screensharingd". If it's marked as block in coming connections, change it to allow incoming connections. 

Be sure to reboot your computer and you should be good to go!