My thinkpad is rather antiquated, and the backlight often takes ages to start up [or just doesn't]. There's a little button that the screen hits when you fold it- tapping it puts the laptop to sleep, and tapping it again usually fixes the light.
Failing that, your screen might just be dead. If rebooting doesn't turn your screen back on, you might not be able to get it working again I would think
There may be a way to do it, see I've heard that some laptop backlights can be controlled through ACPI or dedicated hardware registers, but exactly how you're going to access them I'm not sure. The Linux thinkpad driver* works in this way and can control these signals through /proc. Still, it's not something I've messed about with. And even if you do manage to restart it through some such method, if you've already tried rebooting and that kills the light, you're going to have a great time sending ACPI signals every time your laptop starts.
Is it still under warranty?
* Note that the driver gives the proc interface- the ACPI behaviour of the Fn buttons is enabled even without any drivers installed, the main point of the drivers is masking this behaviour or controlling them through scripts. I imagine it's a similar story for other laptop brands.
was put impeccably into words at DebianDay for me last Saturday, by Knut Yrvin of Trolltech - adults try something once, fail, and then are like "ffs this doesn't work". Children try, fail, and then try again, and succeed - maybe on the second, or even fifth retry. But the thing is that they keep at it and overcome the problems in the end.
-andrewdodd13