Randomly on my laptop screen this appears and debian just freezes. Sometimes these vertical lines don't appear and system freezes anyway. Its just random. How do i identify if this is hardware or software issue? and then how to identify exact piece of hardware or software causing this problem.
RAM or Video card issue. Are you SURE the entire machine actually locks up, or just the display? Try ssh'ing into the machine when this happens to see if it's actually staying alive, though the display stops working.
yeah, entire machine locks up. Yeah have tried ssh'ing from mobile and it was stuck one time when i did that during a freeze. have replugged RAM let's see if system freezes again,