An 'all-in-one' printer is really several separate devices inside a common box. As such, they each have their own drivers. If you can print but not scan it seems clear that the scanner driver hasn't been properly installed.
Reinstall your printer's software, either from the CD which came with it or by downloading and running the file from here:
http://support.hp.com/gb-en/drivers/selfservice/swdetails/hp-deskjet-3520-e-all-in-one-printer-series/5162504/model/5162505/swItemId/al-108812-4
(When installing it, note that some printers require you to choose between a wireless and a cabled connection. If you encounter such a choice, be sure to select the correct one).
Your Bright Box router has 'WPS' wifi connecting disabled by default. Follow the instructions here to enable it:
http://ee.co.uk/help/phones-and-device/home-broadband/bright-box-wireless-router/bright-box-wifi-guides/bright-box-router-connect-using-wifi-protected-setup-(wps)
Once you've got the software correctly installed, and WPS is enabled on your router, press the WPS button on your router and hold it for 5 seconds. Then press and hold the WPS button on your printer until the wireless light starts blinking and for another three seconds. After that your router and printer should connect together by wifi.