VS 2005, virtual keys stops working

In Visual Studio 2005:

Every now and then, at least one time a day, my virtual keys (almost all) on
the keyboard stops to work. All keys that outputs text seems to work fine,
like a-z, 0-9 etc. Even Shift+1 and so on works. But keys like backspace,
arrows, home end, F-keys etc don't work.

When i switch to another program like notepad, all keys works fine. When I
switch back to devstudio, still the same fault. I have to restart Visual
Studio to get everything to work again.

Have anyone experienced this, and have anything found the explanation for
this? Is it a feature? Is it so that I accidently hit some
shortcut-key-combination that causes this?

Thanks in advance