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I saw similar questions but could not find the answer. I will try to give all details. I had upgraded my iMac Late 2012 to SSD - Toshiba TR200. With a Windows installation usb I had to format the drive first then with macOS boot usb I had installed High Sierra by choosing APFS file format. I worked fine, opened normally, restarted normally, I had browsed internet etc no problems. Then I had to reinstall High Sierra with a bootable usb for some reason ( i wish i had not). On boot screen, instead of usb drive, I mistakenly selected third item, i do not remember its name. First was my harddrive, second was usb drive that should have been selected. Now it stucks at white screen. No chime on startup. I hear fans. I wanted to try some startup key options but I think my bluetooth keyboard is not connected, because caps lock light does not work. I do not have a Apple wired keyboard but have a wired PC keyboard. As a last try I have reopened and put my old HDD but it is same. I would be glad if you could share any suggestions. Thank you very much.
You’ll need to use the PC USB keyboard to gain access to the startup keyboard commands: Mac startup key combinations Now you have a few choices here I would try Safe Mode first holding the Shift key to see if you can recover access to the drive. If you have a working bootable MacOS boot drive you could try to gain access via pressing the Option key. In a windows keyboard the mapping would be the Windows Icon key. Your last hope is to use Command (⌘)-R to reinstall the OS from either the hidden recovery partition if your drive has it still or to via the internet (you do need to be connected). As your internet maybe slow at home you might want to just bring your system into an Apple Store to let them help you. Reference: Keyboard mappings using a PC keyboard on a Macintosh
