Are you trying to boot up into Safe Mode, and you’re getting an “Input not supported” error?
Here’s the fix:
It means that the refresh rate that the video card is sending is too high for the monitor that is plugged into your computer. If this happens to you, most likely you are using an LCD monitor (typical LCD monitors can not handle that high of a refresh rate). To get around this, simply switch to a CRT monitor (the old bulky monitors that look like an old TV) and finish what you need to do, or switch to another LCD monitor that can handle it.
It’s weird that a friend of mine experienced this, as Safe Mode has the lowest settings of the native Windows display drivers running. But it happened, and that was the fix.