Wifi stopped working - connected ethernet but no internet

Hi, I have a macbook running El Capitan. Recently, after the battery ran down, when I connected it to the power and restarted it, the wifi stopped working. I also noticed that the date/time had reset to a date in Jan 2016 - so I wondered if that could somehow cause the wifi problem? (It was working fine prior to that, and I didn't change and settings or anything)

I tried a couple of different wifis with no luck, and my phone is still working perfectly with those wifis.

So, I thought I'd try connecting it with an ethernet cable (using thunderbolt adapter), to see if connecting to internet might automatically re-sync date and so perhaps solve wifi issue.

However I don't seem to be able to get internet working via ethernet... In the network panel there is a green dot and it says ethernet to thunderbolt connected (also light on modem for lan/wan port)

Advanced settings

But, when I click assist me and then diagnostics, it shows a red dot and.says failed.

If I click assist me and then assist...

If I enter the details as per first photo it just says

So I wondered if anyone has any idea about firstly whether the date/time could be the problem (or something else??); secondly if so how to fix that whether by ethernet or some other way; if ethernet, how to get it working?

(I tried a couple of cables, rebooting modem and computer, turning wifi off and making sure ethernet is at the top of the list of what network to use...)

Many thanks, Cath