thats an odd problem. i get something similar with wireless adapters but thats because my router is about to shit the bed. first, when you first got the router did you change any setting on it? it's possible (but doubtful) that when the power blinked out it tripped a reset and reloaded all the default settings. if not, try restarting the router one more time. if still nothing, go into the network setting for your lan adaptor and try setting the ip, gateway and dns manually. if still nothing, you onboard ethernet might very well have blown. power surges can do strange shit to motherboards, i once had a short knock out the on board ps2 adapter while eerything else was left in tact.
since you can use a pci lan card, you may just want get a better one. they're damn cheep these days.