Roku Box and Plex (Can't find server)

I have a Roku box connected to my TV.

Plex is as a web page.

I'm signed in to both. All was working well, TV programmes from my desktop going into my Roku and appearing on the screen.

Since yesterday on the settings page on my Plex, I'm getting the message 'Can't find server'.

The Roku box is functioning, ie power wise, but is receiving nothing.

Anyone help?

(NB, the Plex on my ipad shows programmes. So there wouldn't appear to be anything wrong with Plex.)

All solved. Helps if you have a power supply going to the box :)