Vaio VGN-BX760 shift keys dead

Hello to all,
I have been scouring the internet looking for answers to this. Maybe someone else out there can help. I have 13 VGN-BX760 laptops. I have started upgrading them from XP to Win 7 x64. Evrything works fine except for the Shift keys! Neither of them work at all. (actually, the first one worked fine for about 3 months) I have tried new keyboards, nope. I have tried all of the filters and sticky keys tricks, nope. I have called Sony and they say there is no known issue. I find that hard to beleive since it has already happened to 2 of them. Shift keys work perfectly on an external keyboard, so I know it's not the OS.

Ideas?

Have you tried reseating the ribbon cable from the keyboard to the motherboard?

Hey Paul,

First off, thanks. Yes, I did try reseating the ribbon. Actually what I did was fire up a known good machine, tested the shift keys and they worked. I then took that keyboard and swapped it with my bad one. The bad laptop still had the problem (with a known good KB) and the other laptop worked perfectly (with the suspected KB). I then went back to the bad one and reseated the ribbon, just to make sure.

Same outcome...