A grey circle with a slash means that the macOS is not compatable with your mac. https://support.apple.com/en-us/101666
To solve this, you may want to go into recovery mode, by holding CMD and R at the same time. https://support.apple.com/guide/mac-help/use-macos-recovery-on-an-intel-based-mac-mchl338cf9a8/mac#:~:text=Restart%20your%20Mac.,other%20apps%20in%20macOS%20Recovery.
If no hard drives show up in recovery mode, then the hard drive is broken. If they show up and are functional, the hard drive should be good, and you can continue with a fresh reinstall of macOS.