Some motherboards support multiple hard drives. If one hard drive is bootable you can connect the non-bootable hard drive and you may be able to recover the files directly. That’s what I did with my old PC, then the new drive eventually crashed, and I bought a lap-top (the old pc became obsolete anyhow) and I never got around to recovering the data from either of the the two old hard drives.
My computer will allow changes to the boot order in the BIOS setup program that can be run at boot time. I can boot from any of the SCSI devices on the SCSI chain plus the IDE DVD/CD-ROM drive and a USB device. My bad drive is still in the drive bay, and the SCSI controller reports that it can't communicate with the drive every time I boot the computer. Also my old drive makes no sound when normally the drive moves and tests the drive heads during the testing phase. I really ought to take out the old defective drive soon, because it slows down the boot process on my computer.