xp no alt tab in opengl?

Asus geo3 on winxp.

A while back I could alt tab out of opengl games back to the desktop no probs but for some reason I can’t now, any ideas please?

I’ve tried the nvidia xp drivers and also the asus geo3 xp drivers but suspect I’ve stuffed up something in xp whilst messing around.
/slaps wrist

Nothing wrong and everything runs fine but I’m really starting to miss the alt tab function, help!