I have a dell pp12s laptop, when I turn it on with the screen all the way back everything's fine until it goes into sleep mode. Then the screen will not come back on, if I turn it off then back on with screen in normal position it does not work. The screen will only come back on if it is turned on while while laying all the way back.
Sounds very much like a lose video cable (the sleep mode thing is kinda puzzling to me though). If you have an external monitor (or a way to hook it to a flat screen TV) try connecting that way. Then with the screen in a normal (not all the way back) position try to boot the laptop - see if your issues persist with the external monitor.
If the external monitor works, it is a lose connection to your screen. Not the easiest fix but not impossible I think but I could find nothing on screen repair for that unit - you may have to take it to your local laptop/netbook repair shop (or get used to using it flat and turn off sleep mode).
Best I can think of off hand.