Port Forwarding Problem

[#1]

I make the port forward by assigning the HTTP server to a device and it works:

However, after a while it changes to this and the port forward stops working:

This is a problem I really need to solve because it means I can't host my websites.

[#2]

I would suggest using static address as probably what has happen is you device PC-1 has been allocated a new address but the forwarding has remembered the old address allocated to PC-1.
Use a static address outside the DHCP range.

[#3]

How would I do that? I have no idea what a DHCP range is.
dick:quote

[#4]

Make sure the host on your LAN that you want to forward HTTP traffic to has a static IP, rather than DHCP ( it's IP probably assigned to it by your router).  So, check the network card config of the machine concerned.  Make sure you give it a specific IP address and netmask.  Then, if possible, on the router enter that IP in the port forward rules (rather than selecting a hostname).  I'm guessing that is possible with your router but haven't used one for a while.