keyboard behaviour under windows xp pro

I have english keyboard, use both english and french input.I change the keyboard layout by selecting from the language bar of Office XP 2000. After several months, some keys of my keyboard, including the enter key start not responding. I bought a new keyboard, and after several months, the same problem occured again. Likewise, I have so far replaced three keyboard in one year.
Before switching to windows xp pro, I was working with windows 2000 for years, there were no such problems. Is this due to my switching between two different keyboard layouts or is there another cause. Thanks for your help