Happened to me to. I Tried everything, Enabling UPnP, And all other crap, Opening all the ports plus 30 more... Didn't do anything.
Port forwarding conflicts UPnP, so you will want to disable port forwarding before hosting again.
Anyway, looks like your DHCP server lease time is up. To adjust this, you will need to go to your router admin page.
Under something like 'Local Network', click 'DHCP Server'.
There will be a few radio buttons, make sure it is set to 'On'.
It should be pre-configured, all you need to do is set your lease time from what it is on, to something higher.
Hopefully this works. DHCP acts all strange once it's lease time is up.