Windows 7: Keyboard issue - please help

hello

I have a very strange issue on a laptop compaq CQ71 :
the keyboard (internal or via usb) can work on the 'command prompt' windows normally.
but not under vista or seven. In any application I can't type any character. but when I type too much char, I get a buffer overflow ('bip' sound)

I have no bios setting for keyboard. I try a bios 'load default setttings'. same issue.
I have the 'ps2 keyboard' standard seven driver. I try to remove it, at the next reboot it re-install. same issue

same under vista. worked well before.
during the install of seven, I can't write any char in the 'product key' box.

any idea ?