If the IP address you receive from your Internet Service Provider has changed, your access to the admin section will be blocked. This might occur when a "dynamic" IP address was assigned. In that case, you could ask a fellow user with access to adjust the address in the list of the IP filter for you.
To do this, click the "edit" icon.
Then change the IP address and click "Save".
Now is should be possible to login from the specified IP address.