Startup gives a disk read error.

This is a problem my Mom is having with her computer, so this might be slightly vague.
Until today she was having no problems. However, today she turned the computer on,
got the startup blurb, it went to the Windows loading screen but decided to just stay
on that screen with the Windows loading bar just continuing on its merry way.

She decided to restart the computer, the startup screen came up but then it apparently
went to blue screen of death. She pressed whatever key it was and it went to another
screen that said, 'Disk read error - press Ctrl, Alt, Delete to restart'.

Now since I been speaking to her it just goes straight to the disk read error screen
after the startup screen, no Windows loading, nothing.

Any ideas on how to fix this?

You could try my old standby idea. Sometimes a cable connector shakes loose slightly, or its contacts develop oxidation and poor contact with age. Disconnect from all power, open the case, and for each data cable to a drive, disconnect and re-connect both ends of the cable several times. Do the same for the power supply connector to the drive. Check to ensure everything is re-connected and you did not knock something else out or place. Close up, connect power, and try to boot.