All of Lynn's suggestions were spot on.
Lockups are the most common cause. Now what is causing the lockups, that is a different story. If your computer is locking up on a regular basis there is something wrong. Usually memory or software conflicts up to and including spyware and viruses.
could also be hardware issues. Just about anything.
If it happens only periodically and you are using some version of Windows, well that is just par for the course.
I can hear all you Apple snobs out there laughing.
Anyway, make sure you have up to date antivirus and antispyware and run scans for both.
Also make sure you have all the latest updates from microsoft (sometimes and update may actually cause this if you don't update the appliction as well Frontpage in this case) Microsoft is the biggest offender of their own standards.
I hear those Apple people laughing again.Quiet down so I can concentrate.
Also do a complete backup of your important files, because if it is a hard drive problem, you could lose everything without notice.
Sad but true that most folks won't do a backup until they experience a catistrophic failure. Don't be that guy(or gal)
Oh Yeah. If it is a laptop, it could be your battery or power supply causing the problem. Batteries wear out after a year or so and can abruptly shut down if you are not on AC power.
Good luck