Get No response to IP Address via Browser

[Murbella7]

I've read multiple threads around this but never quite the same. My Freenas (running on an old PC) worked fine then one day I couldn't access any data in the pools via my LAN shares. I tried getting into the UI via a browser but the IP address is not recognised. I have rebooted (many times) and checked the allocated IP address for the Web User Interface. So I have two questions. How can I get to the UI? If I can't do that, can I reinstall FreeNAS without losing my pools and hence my data? Any help would be very much appreciated.