need help formatting hard drive

[kuatto]

I have a larger hard drive (installed as a slave f drive)When I click on "format" it starts to process giving me the warning about if I cont. it will erase the driv,etc.I click ok and I get the following

"windows cannot format the drive.Quit any disk utilities or other programs that are using this drive,and make sure that no windows is displaying the contents of the drive ,then try again."

What am I missing?The only thing open is when I went to "my computer" to access the slave drive(f).