Keyboard problem

Any one had this problem or can suggest what might have happened?

Went to upgrade a dell studio laptop keyboard to an illuminated one.

Simple job.

After, I couldn't put my pass word on, eventually found esc, tab, `,1,q,a,z keys wre not working.

Did everything they suggested on line, reseating the keyboard ribbon right down to taking to Cmos battery out to reset the bios and these keys still didn't work.

So I thought it was a dud keyboard, put the old one back in that had work perfectly fine 30 mins before and that didn't work, with exactly the same keys not working.

Did a scan and it said 2000-0411 cables keyboard not detected.

All the other kets work as normal.

Thanks.