No longer get a signal to pc via the digital connector

I have 2 pcs connected to 1 LG monitor - I digital & 1 analogue connection simultaneously.

I updated the avg on 1 pc today & re-started the pc. I can no longer get a signal to this pc via the digital connector but it is fine via the analogue one to a different pc. Ive tried disconnecting & re-starting but still nothing.

Ive never had this problem before so looking for any quick fix I can do myself?

Thank you!