Bob is having problems with his computer becoming unresponsive. It suddenly freezes up until he reboots it. Leo says that it may not be crashing for freezing at all. It may be an unresponsive mouse or keyboard. If the clock continues ticking, then it hasn't crashed. But if the clock is stuck, then the processor has halted. Even then, the processor may just be busy and he may just have to wait. He'll want to be sure it's really halted, though. If he reboots the computer in the middle of reindexing the hard drive, it could corrupt his drive.