turn off the computer. Turn it on. when you see the white text on black screen (BIOS) start tapping F8, get into safe mode. Do you still see the screen as purple. If so then something happened to the GPU/IG on the laptop (it is a motherboard/video card issue). Check with the manufacturer if under warrantly. More then likely they will have you (if it is still purple in SAFE MODE) to insert the Windows RESTORE DVD to wipe your computer back to when you first got it (yes you lose all your 'stuff' on the computer), and if when the RESTORE DVD starts it still purple (i.e. I can't even click anywhere even when I see my mouse) then that prove it is a hardware failure.
If this is a old computer, well, time to get a new one.