Unable to change the letters of my HDDs

Hello,

Let me explain my problem: I have 2 hard drives, with Windows Vista (and Linux, but that's not important) on the first one and 2 data partitions (my documents and important files) on the second one.
I disabled the second hard drive to perform a procedure without deleting my data, but when I reactivated it, I forgot to remove my USB key that took the letter F:.
The problem is that my important files were on F: and my documents on G:. Given the presence of the USB key on F:, Windows assigned my important files to letter G: and my documents to letter H:. I had made all the necessary redirections for my documents according to G: and I wanted to place my documents back on G:. Using the Vista disk manager, I only had time to change H: to I: (my mistake) and since then it doesn't want to change the letters anymore, showing me an error message: "Incorrect parameter."

Could you help me change the letters? (Hoping I didn't confuse you too much ^^)

Thank you in advance for your answers!