Hypixel works for some reason but some other servers don't like Jack's server doesn't work for me either. All it says is "Can't resolve hostname" so I don't know what is happening to Minecraft. I even uninstalled it and reinstalled it and still didn't work :/
Try clearing your DNS cache. If you are windows you open command prompt and type "ipconfig /flushdns" without the quotes. Or you can just google a guide on how to clear your DNS cache.
You can also google how to set your DNS server to Google's.
These 2 things generally fix this issue 100% of the time.