Hi, I have an old laptop, sometimes it just randomly crashes and goes flashing colours like the attached image. Might be when I’m processing lots of things. A diagnosis and solution would be very helpful. Please look here: Image Video
it might be getting hot or the gpu could be getting hot bad ram maybe. clean the laptop open it up and clean all of it using a non conductive non corrosive liquid with non abrasive static friendly cloth or wipes . i had a laptop one time that the screen would start flickering but it was a lose lcd cable.
Is it getting hot? As you said it's old, it could have some dust inside of it, so remove the case and have a look, also try to change the thermal paste.