Laptop graphics problem

My laptop (Dell Inspiron 8500) came with a WUXGA display (1920x1200). It's just 7 years old, but has performed well until now.

Recently I started seeing video distortion: sometimes it was as if the display was "wearing thin", with pinholes appearing behind the wallpaper. At other times it would go "blocky" - quite coarse square blocks of solid colour. When it did this it would rapidly stop responding.

Tried an external monitor - same effect. Ran Memtest - no problems. Tried the Dell diagnostics: nothing found. Happily I'd recently (hours) done a full backup, so I migrated everything to a spare machine.

I passed the laptop to a neighbour, who does "component-level" repair, and has fixed machines for me in the past. He hung onto it for weeks, but eventually traced the problem to the graphics card; sourced a component from China and replaced it. Seemed to be ok when I checked it out. However, now I've tried to use it in anger, the problems have returned, and I've just shut it down by holding down the power button as the display was flashing on and off every second or so.

One thing puzzled me - the driver utility is now telling me that the display's maximum resolution is somewhere in the region of 1280x900 (forget the exact figures, but well short of the original resolution. I downloaded new drivers and graphics-card bios from the Dell website, (identifying my machine specifically by its service tag); I reinstalled the driver (no change) and the bios cancelled the update when it identified that the same version was already installed.

Time to give the laptop a decent burial, or is there anything else worth trying?

Phil, London