求助: How can I solve this problem?

I was trying to format C disk. It says: Format cannot run because the volume is in use by another process. Format may run if this volume is dismounted first. All OPENED HANDLES to this volume would then be invalid. Would you like to force a dismount on the volume?

I typed "Y".

It says: cannot lock the drive. The volume is still in use.

How can I solve this problem?