1. Check if the Drivers for the Graphics Chips are intact . Also try and Connect the system via an External Monitor and see if you have thesame flickering Display.
2. Remove ,clean the RAMS with 90% Propanol . Also clean the RAM Slots on your system with a clean Brush. Reinstal the RAMs one after the other....
3. If problem persists ,try another RAM that you know is functional .
4. You may also remove the battery , hold down the Power Button for 60 Seconds ( without power cable) . Connect the Power Cable (without the Battery ) and TURN it ON . You may repeat Step 4 with Battery and Power Cable and Turn it on .
5. If all of the above do not help, it may be a GPU related Problem .