I've got an external monitor hooked up on my laptop. If the monitor is plugged in when I boot, any time before Windows loads, the laptop screen is disabled, and is not recognized even after I log in (so Fn-F4 is not an option). There's nothing in the BIOS regarding screens.
The easy workaround is to unplug the monitor before booting up and plug it as soon as Windows stars loading, but that's got annoying very fast, especially on soft restarts. I'm looking for something a bit more permanent.
Laptop make & model is HP G72, Windows version is Home Premium 64b SP1 and display adapter is listed as Intel HD Graphics.