Have you reinstalled 68040 or 68060.library? This might be the reason why the computer locks up.
As for the games, try downloading Warp3D instead. This will show you the power of the PPC CPU compared to the 68040 or 68060 you are using. Needs a graphics cards as well IIRC, but you already have that; maybe you will be able to see the demos despite your current issues...
