Top 2 rows of keyboard not working - Latitude E6420

Hi,

I have Dell laptop where I faced problem with Keyboard as follows:

While I was using the laptop, keyboard was working fine and then one by one almost all keys of top 2 rows (i.e. function keys & number keys-without pressing Shirt key) stopped working.

I was renaming files when it happened. Suddenly I couldn't delete character using "Delete" key and next was "Home" button which stopped working. Next were number keys which stopped and all of this happened within like 30 minutes.

There are no external device attached except external hard drive. I removed external hard drive and rebooted the system. I have removed battery and placed it again.

I formatted C: drive and reinstalled Windows Pro 7.

Even after all of these actions, top 2 rows of keyboard is not working.

Do you think it could be hardware problem? How do I know for sure that replacing keyboard would solve it?

I tried running quick diagnostic tests from Dell site but it didn't work. System Detect tool is not getting installed and hence diagnostic test is not working.

Can you please guide me how to fix this problem?

Thanks & regards,

Ajit