Keyboard issues

[Dragutin]

Hi all, I've got a very strange issue.

My computer won't recognize the "shift-z" command. Shift and any other key works and the lower case z works. Only the key combination shift-z to produce a capital z does not work. Hitting caps lock then z is the only way I can get around this. I'm on Windows 7.
Right now I have a MS Sidewinder X4 keyboard. Before this, I had a Saitek Eclipse II. This problem started popping up in the last week that I used the Eclipse and disappeared with the X4. It has since returned, though, and I have no idea how to fix it. Has anyone had experience with this type of thing?

Thanks

 

[Dragutin]

I went to Control Panel > Ease of Access > Ease of Access Center > Make the keyboard easier to use. All the options are off, but my problem still persists. Is there a different area that I need to look in?