OK, this one was posted a while ago by another user, but

I have experienced a slowdown in 3d and even 2d games.
GLXINFO reports the following on direct rendering:
direct rendering: No (If you want to find out why, try setting LIBGL_DEBUG=verbose)
However it told me that direct rendering was on until yesterday.
Is there any reason for this to happen?
My video card is Via Unichrome IGP KM400 and I am on Ubuntu Gutsy Gibbon.
Does anyone know how to re-enable direct rendering?