I installed CCleaner Pro to erase the hard drives of my computers. I went to tools and clicked on the entire drive and also the advanced overwrite. I could not click on the C drive box or icon or the 'wipe' button. Any help or suggestions? Thanks.
See here
https://www.piriform.com/docs/ccleaner/using-ccleaner/wiping-free-disk-space
Entire Drive will erase all of the files on the drive. WARNING, this means the whole of the partition will be erased. The drive will still be formatted, but all data will be erased. For safety reasons, this feature is disabled for the boot drive.