Toto power gravity problem

I have a toto ultimate toilet with power gravity flush system. It keeps flushing - the tank keeps filling (over the level where it should stop) and it keeps flushing. Any ideas?

Sounds like you may have some dirt/sand/crud in the washer that seals the toilet fill valve, preventing it from shutting off. If you do a little search here, you'll find the maintenance info on how to disassemble it. Toto uses (mostly) Korky fill valves.