A fact for your consideration : HDDs work something like an old time record player. Record players had a "Tone arm" with a needle that was in contact with the record, and read the record by vibrating as it passed through the wavy grooves cut in the record. When you wanted to change the record you would put the "Tone arm" on its stand, so it was no longer in contact with the record before changing the record.
HDDs, have"Read Write Heads" that are not supposed to ever come in contact with the spinning platters beneath them. Instead they are kept floating just above the surface of the platters by an air cushion generated by the spinning of the platters, and they read and write information to the platters magnetically. When you use the Windows shutdown or restart procedure, the "Read Write Heads" get "PARKED", (similar to putting a record player "Tone Arm" on its stand), before the machine gets powered down, thereby preventing the heads from coming into contact with the platters.
BUT when you just power off the machine what happens is the "Read Write Heads" are still out over the spinning platters, when power is cut off, and the platters start to slow down their spinning, and the air cushion that supports the "Read Write Heads" collapses, and the Heads fall into contact with the still spinning platters. This is what is known as a "Head Crash" and YES it does damage the HDD, because typically the Heads bounce back up then fall back down several times, before finally scraping to a stop.
SO : 1) Use the windows shutdown procedure whenever possible. 2) When not possible use the Control Alt Delete key combination to bring up the Task Manager window and use it to shut down. 3) When that isn't possible use the power button, but have it set for the "4 Second Delay" so as to leave time to "Park" the "Read Write Heads"
If I were you, and you have a Windows XP install disk, what I would do is replace the HDD then reinstall Windows on the new HDD. You probably will not be able to salvage any data off your old HDD, so in future : 1) Follow my instructions above. 2) Ideally install a second HDD to keep backups or "Ghost Images" on, so in the event of future problems you can restore your Windows partition.
Edited by JHMcG, 22 April 2013 - 08:26 PM.