How do I change drive letters?

GeForceG

Banned
Dec 21, 2001
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I have 2 main HDs. One is D: and the other used to be C:
Now C: turned to G: for some reason, and everything got messed up!
I am using Windows XP Pro and in Computer Managment I tried to change the drive letter and it tells me that windows can't change the drive letter of a boot or system drive. HOW ON EARTH DO I CHANGE IT BACK TO C:??

PLEASE PLEASE PLEASE HELP ME!!
THANKS!