Did you ever re seat all the hardware as I suggested earlier in the thread, it is possible that the gpu is loose. Re seat all of the hardware components and get a can of compressed air and spray out any dust while you are at it. Just make sure and turn off the computer and unplug it and wait five minutes before removing anything.
Can you take a picture of the inside of your computer and post it here.
Can you take a picture of the inside of your computer and post it here.