Q: SOMETIMES COMPUTER STARTS UP OTHERS GRAY SCREEN

My computer will flicker a one two or even three times then go to a gray screen. Sometimes it stays on gray screen for a while the shuts down and restarts on its own. I have tried starting in safe mode, sometimes it work sometimes it does not. I have had 3 or 4 yellow stripes from top to bottom equally spaced. I have had it stay on a gray screen, gray with yellow stripe screen, black screen, very small boxes green screen, very small boxes red/pink screen. I have repaired permission from backup drive and internal drive and repaired disc, no problems. If there is any help I would greatly appreciate it.