New battery, new alternator, yet car has absolutely no electrical power what could be the problem?

Recheck battery cable connections .. Possible blown main fuse if short circuit OR 'reverse polarity' occurred while battery/alternator was being installed!!

Does the horn work?If no, check cable connections. If yes check for power at the 7.5 amp a/c compressor fuse. If no power then the main 150 amp alt fuse is most likely blown. some times its hard to see on lexus vehicles. Jumping a vehicle backwards is most likely the cause and may have other blown fuses.