Formating a primary (not root) partition under WIN7

[amosiman]

Partition F in my PC was once installed with a second Windows' and was not erased correctly.
Now I hace WIN7 on my C partition, and PC works fine. I want to clean/format the F, but unable.
What should I do?

 

[amosiman]

The former OS was either WIN7 or VISTA. If WIN7, it might be the STARTER software that MS supplies for testing WIN7 befor purchasing it. This PC was not in my hands, so I am unable to know its history exactly.
The system cannot be booted from F.