I think Unknown_K might have the right answer -- if you have changed the hardware configuration after installing the OS, things can go awry. The installed software may look for the FPU just once, during the initial install. After finding it, it may make the assumption that it remains there, instead of wasting cycles rechecking every single time it undertakes a calculation.

So, you may have to reinstall the OS to get it to start behaving properly. I am not certain at all about this, but it seems reasonable.