Ok Senko,
Rather than put you through more 'pain and suffering' ...It's now my turn for the bad news
You have two choices here...
1: Go to the Hard Disc Drive's Manufacturer's website and download their HDD Diagnostic tools and run that on your computer...this will determine if the HDD's are actually 'damaged' as a result of being 'bloated' for so long.
If the "Tools" say that the HDD is OK then, you are extremely lucky...if they say that they are 'damaged'; it's this...
2: Get what ever files you want to 'save' to that external HDD; then go
here, and download "Boot N' Nuke", a program that will completely wipe your HDD; then, it's a 'fresh' Installation of Windows® XP Home for you.
One Important Point: If the Diagnostic Tools
do show "Bad Sectors", "Boot N' Nuke" might or might not help

...if not....then it's a trip to your friendly computer parts store and buy some 'new' HDD's.
Sorry for the bad tidings.
Kind Regards,
__________________
Dave T.
If it works, Don't fix it!
Especially if Bill Gates had anything to do with it!!