Ok, so I've got a Windows 95 machine which tells me "Windows has detected a registry configuration error", and prompts me to boot into safemode at the boot menu. The problem is, it won't boot into ...

I think it would depend on the motherboard. Some can make a USB drive appear as an INT 13 device, and I've seen some USB drivers for DOS.

This article highlights the issues that older computer systems will encounter when the Secure Boot Certificate expires ...