i cannot reset to factory settings

Hi,

Not sure how old your iMac, though following tips could help your issue.

What to do before you sell, give away, trade in, or recycle your Mac - Apple Support

If it doesn't help, start up in Recovery mode, then reformat internal HDD with DiskUtility, then reinstall macOS.

Use macOS Recovery on an Intel-based Mac – Apple Support (AU)

iMacs covered in this forum section were made before 2006. Is yours that old?

How to do what you ask depends on the iMac family to which yours belongs. There are five families dating back to 1998!