I have the exact same problem; there was a power cut to the house and the power was off for about 24 hours. Everything (imac, macbook pro, printer, router, airport) have all come back online and are functioning normally, but the roku can't find the wireless signal. I reset everything, but when I came to the wireless setup screen, there was NOTHING; the row of selections that should be there was blank. I've
1) turned everything off and back on in the right sequence (router, airport, computer then the peripherals; printer, roku) and I've
2) performed the factory reset that the ROKU help desk suggested (40 seconds; unplugged 10 seconds) it has absolutely NO effect.