Bootmgr image is corrupted: system won't boot (Windows 8.1)

Greetings. A friend of mine is running into the exact issue described in the title. He powered down his PC, intended to turn it back on after a few hours, but now he’s being met with this specific error message... Since he still has a Windows 8.1 installation DVD lying around, I suggested he attempt a system repair, but the machine simply refuses to boot from the disc. When the prompt appears asking him to "press any key to boot from CD or DVD," he hits Enter—or tries any other key—but the screen just hangs there on that sentence and nothing happens at all.

He also attempted to trigger Safe Mode via the F8 menu, but that option won't even show up. This is a desktop unit... He went as far as resetting his BIOS settings to their factory defaults, but that yielded absolutely no results. Does anyone have any actual advice for this situation?

Tell him to double-check those SATA cables—make sure they’re actually seated properly—and he should probably do the same thing with the RAM modules just to be safe.

Zero points... honestly. I’m planning on dropping the PC off at the repair shop this Monday, though I’d much rather find a way to avoid the hassle. I just can't wrap my head around why he can't get a CD to boot. He even tried a bootable drive with Windows 7, but it wouldn't stand a chance of running. Legacy mode is enabled in the BIOS, so that shouldn't be the issue, and he's still using an old-school PS/2 keyboard 🤷

Is it a bootable USB?

There isn't another computer nearby that I can use to create a bootable USB drive... Honestly, he could just drop it off at a repair shop, but it feels like a total waste of money if they're going to charge him for a "fix" when there's practically nothing even broken... (that's my hope, anyway)