Ok, makes no difference to the overall result. If the browsers etc are configured to use a proxy server, that proxy has to know about the site, and possibly be configured to allow access to it.
I find the static/DHCP situation interesting however, as that would imply that the static IP address is not correct for your setup? As soon as the IP address is assigned by the wider system, all works, yet a manually configured IP does not?
Surely suggests either a problem with the IP address, or that the DHCP system is setting gateways, proxies or something similar?