It appears many HP laptops (including my dm4-2035br) boot Linux kernels with KMS enabled with the screen backlight set to zero. The screen appears blank, but you can see the image if you shine a flashlight on the screen.
If you have the this problem, you can workaround it by adding the following kernel command line:
video.use_bios_initial_backlight=0How to do it varies from distribution to distribution, but on Fedora you can hit TAB on the installer screen and type it after the other options.
If this solves the problem for you, it might be a good idea to file a bug in Kernel Bug Tracker (under ACPI product).
Update: This bug is solved with the release of kernel 3.12