I always have my iMac on and this morning when I started it from sleep I was asked to choose the language just as we see in the fresh install screens. After selecting asked me to back up from Time Machine. Before I had the buggy 10.7.3 and then I re downloaded the right 10.7.3 from apple website. Since I had the Wifi woes, I did a pvram reset and nvram reset. Both of them didn't help but no issues on OS by then. What could have caused the OS to re install by itself?