Try Disk Utility first. If that doesn't solve things, you can reinstall the OS. The software is downloaded from Apple and installed automatically; no disks were provided nor needed for Mountain Lion.
Shame on both of us, Jon, for forgetting to advise Rita to rerun "Repair Disk" until she got either an "all clear" or a persistent, uncorrectable error.
The new Great Equalizer is the SEND button.
In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
