If you are using overdriveNtool it sounds like its Windows based.
When you run that many cards you really should be using linux. I have hundreds of 12 card linux rigs that are ROCK SOLID running the H110 board.
My personal and our company miners run PiMP
https://bitcointalk.org/index.php?topic=558715.0I have uptimes approaching 250 days on these rigs!