Ok so, I was playing an online game on my HP Pavillion 6500 when suddenly a purple screen with pixilated squares appears. I reboot the laptop and now when it's starting up all I see is strange pixilated screens (usually black, with squares) similar to TV static. It does not respond to any input and doesn't get to the windows logon screen. I have tried connecting the laptop to a external monitor, but it seems that the laptop doesn't recognise it.

I'm just wondering what hardware part has died and what the problem might be?

It sounds very much like your onboard graphics chip has died to me. Unfortunatly with laptops it usualy is a matter of replacing the whole motherboard.

You could try a cmos reset, which i think is done by removing the battery and holding down the power button for 5 or so seconds. Also make sure there is no dust or crap blocking any of your vents, and a good blast of compressed air cant hurt.

Hope this helps

I guess you have nvidia 8400 gs in your laptop. There could be warranty extension on your lapto for the problem you experienced so check with HP on motherboard replacement. People had fixed your proble out of warranty by baking it in oven or applying heat from heat gun to nvidia. Best option is to send laptop to somone who has the tool to remove nvidia chip the reball it with lead based solder and put it back. You looking at about 90.