First of all, don't panic, and only do ONE thing at the time! Nothing is changed or lost on your receiver.
As DD said; changing the router has nothing to do with anything on your box, except the network settings, that have to be updated ONLY IF the new router is on a different IP address range, which is probably the case.
Go to network settings on your box, tick "Use DHCP", save, exit, reboot.
Go to network settings again and check your connection.
Since you do not seem to fiddle much with the box, it's fine either way.
- If you play with it a lot - FTP, Telnet, channels editing, files, etc. and you know well what you are doing and can diagnose the problems; fixed IP might be a bit more suitable
- If the box is only there so that you can watch the TV - leave it on DHCP Enabled (ticked = ON), at least it will save you the trouble of going through this again the next time something changes on your LAN.