|That's a mean computer, not allowing you to do something.....I'm assuming it's a newer PC with SATA HDDs?|
1. Make sure you have all your old data copied over to new HDD first before you format the old drive ("C").
2. So I'm assuming you want to use the original HDD (old "C") as a backup hard drive? If yes, you would have to make your bigger HDD ("F") your main HDD that your PC boots to. Then make the old HDD ("C") a secondary drive. You would do this in your BIOS.
3. Then in Windows Disk manager, locate the OLD smaller HDD drive and do a format on it.\
If you do not want to use the old HDD as a backup, you just put in another PC and boot with the OS DVD/CD and reformat it in the Windows installation process.
MOOOOooove! OH and you're welcome!