Oddbean new post about login | logout It may not be connected to the internet, so try and ethernet connection. And then it may be connected, but has a different IP address than before, so log into your router and look it up to ssh in.
Did you change your router? Quite likely the issue is as described by Jay. To find the new IP, you can either go to your routers admin console, and look at the list of active DHCP leases. Did you give your RPi a name? If so, that name should show up here. If there are no names, OS should be mentioned. Find the ones that say Linux, and try to login in one by one, when you have the correct IP, login will succeed.