Have you tried resetting the router. I don't have experience with this, but sounds like the router is still off-line since the power outage, and can't authenticate the tablet's connection request. I'd try a simple reboot of the device before changing any settings.
Thanks, the link on troubleshooting ICS was useful. One quick question for my own knowledge - when you got this to work, does the router remain hard-wired to the PC?
How do I reboot the device? I did switch it off and on again. Would that suffice?
Yes it does as the PC does not have a wireless receiver/transmitter on it.