reset TCP/IP setting

If you don't recall how it was before applying the change, you probably would want setting it to obtain everything automatically via DHCP, IP address and DNS server settings.

Nevertheless, an internal static IP address should work as well, as long as you took a unique one from outside the DHCP range of your router.

And no, there is never a "workaround" for configuration mistakes. ;-)
You simply have to do it right.

Yes.

If you want a more detailed answer you'll need to provide more detail in your question. Your question as it stands is a bit like saying to a mechanic "My car made this strange noise and stopped, is there any way to get it going again?" and expecting them to tell you exactly what to do to get your car running.

I'd start by checking that you've correctly configured your netmask and default gateway, and that your router is forwarding the relevant port(s) to the static IP on your network. I'd also suggest you work through this wiki entry.