then the problem was slightly more convoluted, possibly the date was an issue, or maybe the PC was unable to broadcast its MAC address due to the battery screwing up the BIOS. Or maybe the last IP address is normally held in the CMOS but couldn't be due to the battery....(guessing there)
either way, the machine would have been self-allocating a public-range IP address rather than being allocated one by the router, so couldn't communicate