1) Try to get the newest drivers.
2) Install the latest directx.
3) Try different video modes (OpenGL, Direct3D)
4) If all of the above doesn't work get glsetup.
The Web setup installs only what do you need, the monolithic setup is an 88Mb file.
Problems reading halflife.wad? Mmmmmhh....try to make a deep level scandisk, your HDD might have little problems