Context issues

I am just getting started with WebGL. I am using a Windows 7 platform and for several days everything has been working fine. Suddenly I am no longer able to get a 3D context using either Firefox or Chrome. The utility that I use requests a context using the strings: “webgl” “experimental-webgl” “webkit-3d” “moz-webgl” They all fail, where just yesterday they worked. Anyone have an idea of what could have changed?