Vostro 1500 Keyboard / Media Buttons Issue

About 4 months ago, I started travelling so I haven't been able to address this niggling but incredibly annoying problem properly

About 6 months ago, when I turned on my computer, I noticed that my keybaord had stopped working. The media buttons on the front of the laptop worked fine and so did the touch pad.

I immediately turned the laptop off and rebooted and the keyboard still didn't work. However, after a couple more reboots it began working again - I thought notihng more of it.

Fast forward another 2 months and the issue re-occured, and despite reboots the keyboard still refused to come back to life. I took the laptop apart and reseated / took out and re-inserted the keyboard connector and it worked well again for about another week. Then, the touch pad, media buttons and keyboard all stopped working.

In the 4 months since that happened, the touch pad has come back to life, but the media buttons and the keyboard all refused to work. Recently I ordered a new touch pad / wrist rest assembly AND a new keyboard from the internet. They arrived and last night I tried replacing the wrist rest and the keyboard.

Lo and behold, the same thing! The keyboard and the media buttons do not work, but the touch pad is fine.

The system is a stock Vostro 1500 (2.0GHz Core 2 Duo, 4GB RAM, 8600GTM, 160GB HDD, DVD etc running Windows 7 Ultimate).

Can anyone shed any light on this issue? Is it a connector issue? (motherboard to Touch Pad / Keyboard PCB) or is it a individual component error (media keys / keyboard. I find this unlikely as its a new keyboard and palm rest) or do you think it's something more terminal (like a logic controller on the mother board has shorted / died?)

I can buy an external keyboard, but it means my laptop is no longer portable / useable and I really liked being able to control volume / play / pause with out a mouse click and using the front keys.

Please help and many thanks in advance of any advice you can give.

G