Screen flickers and then goes black after a few minutes, any ideas?

I have an Inspiron 1150 laptop, it turns on ok, then after a few minute the screen flickers once, than after a few more minutes it goes black (however if you shine a strong flashlight on the black screen you can make out that it is still very faintly displaying). I tried hooking up the laptop to an external monitor, and the monitor kept saying "power save on press any key or move the mouse.etc" even when the display screen was working OK on the laptop (the first few minutes after start). Pressing a key on the laptop did not change the message on the external screen. I did notice that 93% of the space on the drive is being used. Any ideas?