Very long shot...
If you have the type of computer that has a "software" switch, i.e. it has a "start button" and you can put in a command that turns off the CPU, as opposed to a big throw switch, try turning it off and actually pulling the plug, either out of the wall or the back of the machine. Give it a few minutes, then plug it back in and try again.
This REALLY clears out whatever unknown memory is persisting in various things, and sometimes...just sometimes...it clears out a bee the computer has in its bonnet. This actually worked for me once when my computer was not booting.