Hello, I have an 2012 21.5" iMac which recently had the drive fail. I purchased a new drive on eBay and popped it in the computer, expecting to boot off of an external drive to format the disk and install macOS. Unfortunately, the computer instead booted to the copy of Windows 10 which was installed on the new HDD I had purchased. At this point, the computer stopped showing the apple logo or responding to any normal commands such as holding option on the chime or booting into safe mode etc. I was using a wired keyboard before you ask so the bluetooth connection was not an issue. At that point, I removed the windows disk, wiped it using my MacBook Pro and installed high sierra, the put the disk back into the iMac. Instead of booting to the disk, however, it boots to a Windows recovery screen, which has the code 0xc0000225, which is pertaining to not finding system files for booting. Go figure. Still cannot use any apple commands on boot. Any advice? There doesn't seem to be any real resources online for this.