Originally Posted by
persianpenname
The happydiggers public server, right now, is still on TFC build 78, which is based on minecraft 1.6.4. They're currently getting the next iteration of the server (TFC build 79, minecraft 1.7.10) ready for public release, but it's not ready right now. If you look at the stickied thread asking for builders, they explain what's going on with that.
To sum up, you upgraded to a version of minecraft and TFC which is not what happydiggers is currently using, so yeah, you won't be able to connect to it.