The symptom is in line with a failing motherboard or LCD panel. If it was software the BIOS screen would work which it sounds as if it does not.
To eek out a few more months folk sometimes plug in an external monitor.
However http://laptops.reviewed.com/products/toshiba-tecra-r840-s8440/specs notes a 3 year warranty. Check your receipt.
My computer (a Toshiba Tecra R840-S8440) shows a white screen when I start my computer with random lines. The white screen then fades into black. Anyone know how to fix this?
Here are the photos:
(first image is the white screen and the second image is the black screen) (sorry I didn't post picture of it fading)