You'd better confirm with your printer's technical support if there is another way to add it to a new Wi-Fi network. Sometimes, pressing the button is not a good way to connect to Wi-Fi sometimes...

What's your test result? Can you provide some screenshots?

It is quite normal according to my understanding... http://forum.tp-link.com/showthread.php?81227-Poor-5MHZ-Range

Go to System Tools---Factory Defaults to Restore. If it cannot be displayed, hard reset it by pressing reset button for 10 seconds. Later, try the web interface again. If it is the same, try to get a...

That's Weird... Can you provide a screenshot of the error? The router is a brand new one?

Who is your ISP? If your ISP provides PPPoA as the connection type, DO NOT change it to bridge mode as WDR3600 has no PPPoA as the connection type. After you make the modem work, to configure...