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The file system on the boot drive can become corrupted if, for example, Windows isn't shut down properly (power-outage, switching the PC off while Windows is running etc.). Since this isn't physical damage, Windows Check Disk is able to rectify it. It's very likely that if you were now to put that disk back into the PC it came from (as the master), it would boot into Windows like it used to do. Since that is now unnecessary, you could put the disk back as a 'slave' into the PC it came from, and your parents could use it as a backup for 'My Documents'.
In other words, it's very probably a perfectly healthy disk, but just to be sure you can run the disk manufacturer's diagnostic tool on it. Take note of what make the disk is, then visit their website->support area. Since the disk only a slave, you can run the diagnostic tool from within Windows where a Windows version of the tool is offered.
Links to some of the most popular hard disk manufacturers support/download areas for USA:
Western Digital: http://support.wdc.com/download/
Finally, if you do end up scrapping the disk, or indeed any disk, it's unwise to simply toss it in the bin. It could hold confidential data which others could access (and they frequently do). Before removing the disk you should run something like 'Darik's Boot And Nuke (DBAN) on it, using the bootable floppy that the DBAN download creates for you. Either that or physically destroy the disk, which isn't easy as they are built like mini-tanks!
DBAN is free, and you can get it here: http://dban.sourceforge.net/
Edited by pip22, 26 November 2007 - 02:19 PM.