MacBook Pro 15" mid 2010 backlight is on but no picture.

Had the computer in my bag sleeping. Attempted to put my bag on. The bag strap broke and the computer fell in the bag on to the ground. Took the computer out and it was damaged a little on the top case side cd rom side, near the lower corner next to sleep/wake light. The sleep wake light was normal. Everything looked normal except the screen. The screen look lit up but no picture. I hit the dimmer all the screen did was get lighter and darker. The keyboard was working normal, sounds, caps button, power and charger/charging. I restarted by holding down the power button. It started up and when through the normal process. I seen the apple logo and then it went to my desktop screen. As soon as my desktop popped up then the screen turns black but, it seems illuminated. I plugged in a vga adaptor to the display port and a external screen worked. I mirrored the screen with the command F1 key press. I could us the computer with that external monitor like a desktop. As I use the computer the laptop screen would flicker picture in and out and when the windows i used where full sized picture would also flicker back to the laptop occasionally. I took it to Apple and they didn't diagnose the problem they just said they would change "parts" cause they don't repair they just replace. and some high number figure on a work order which I declined I couldn't pay for.

they said the hard drive was normal and wasn't damaged that was it. To me it sounds like something is loose or getting poor connection or is shorted on the logic board from the fall. I put a new hard drive in which i updated to latest iOS with the 15" MBP. I swapped my orginal hard drive to a 13" MBP. Same results on 15"MBP with new hard drive no picture, the 13" MBP now has my original hard drive in it and has no issues. Still trying to get the 15" MBP back to normal.