If you turned off your DHCP server follow these steps to connect to FritzBox settings.

• Set your computer IP to 170.254.1.2 and your mask to 255.255.0.0
• Then go to 169.254.1.1, login and re-enable the DHCP server:

On gnome turn the wired connection off on again to apply the settings.

Note: why in the hell does FritzBox 7490 require a land-line telephone to be physically factory reset?