Could be as simple as a loose connection! My 3 year old Sony Vaio had similar beahviour after repeated dropping (just careless I guess!) Some work with a small screwdriver and an inquisitive nature led me to dismantle the beast where I found the loose connection to the screen. Put it all back together with no bits left over, and it now continues to work perfectolkzxdjm .ksjebv.,mdasnfv ............
All done within a couple of hours in a dimly lit hotel room.
