hardware problem... suddenly became sensitive to impact, what could it be?

My cheapo laptop has been serving me well and its been through many upgrades since 2005, but just the other day, it blue screened and the screen showed artifacts that change patterns with physical impact.

It just happened suddenly. I didn't drop the computer. It is not a driver issue, because the artifacts can happen in "HP invent" BIOS splash screen too. Sometimes the CPU fan would spin at full speed and screen doesn't come on at all

I tore the whole thing apart, connected LCD panel, memory and external mouse and assembled the thing on my desk without casing. I tapped on the board with a plastic pipe in several places and I couldn't duplicate the problem, all the the board is not placed under same strain it is in when its fully assembled.

I inspected for points where case shielding maybe shorting to something. Couldn't find any.

I reassembled the computer and problem is back.

What could this possibly be? It was working perfectly fine until a few days ago!

 

What laptop is it?

 

It's an old Pavilion from 2005. ZE2000 series