What would be the most common reasons to get a plain black screen?

[Dr Pepper Can]

Could it be that the rEFInd file became corrupt?
The only way around that I can think of is to try to access the BIOS and change the drives booting order, whether rEFInd can be loaded or not. Just to regain access to Windows.
But I would love to know if there is a way of getting rEFInd working again.

Thanks,

DPC

[Roderick W. Smith]

Several things can cause this, but if rEFInd worked before and has stopped working without you doing anything (like upgrading rEFInd), then my top guesses would be (in no particular order):

• Filesystem corruption on the ESP or a damaged rEFInd file
• Filesystem damage off the ESP, but on a partition that rEFInd can read because of an EFI filesystem driver
• A change to the EFI boot order such that rEFInd is no longer booting by default, but something invalid or buggy is
• Activation of the Secure Boot setting in the firmware, if rEFInd is not properly configured for it
• Corruption of the firmware or its settings

You can investigate these options one at a time -- for instance, by running a disk check tool on the ESP or other partitions, re-installing rEFInd, examining the boot order with efibootmgr in Linux or similar tools in other OSes, etc.

Most computers offer a way to access the EFI's own boot manager, thus changing the boot order on a one-time basis. You can use this to boot another OS to do work or to further investigate the problem. Unfortunately, details vary from one computer to another. On Macs, it's done by holding down the Option (or Alt) key while starting up. On most UEFI-based PCs, it's done by pressing a function key at a critical point in the boot process, which which key it is varies from one machine to another. (It's usually a high-numbered key, though, like F8 or F11.) Sometimes hitting Esc or some other key serves this purpose. If you're lucky you'll see a prompt appear saying what key to press early in the boot process, or it will be documented in the owner's manual. If you're not lucky, you'll have to try randomly or ask on a forum dedicated to your motherboard or computer brand.