|The exception to the above is if you have placed the computer in one of the power saving modes that allows the hard drive to stop. |
The typical hard drive is rated to have an average failure time of at least 100,000hrs. That is over 11 years. Some drive series have an average failure time of over a million hours.
Unfortunately this means that some may fail right away while others will seem to run forever.
Failure can mean different things. Data corruption that is correctable wouldn't be considered a failure.
Back up your data.