When I start to play WWP (with CPU or on WN) the screen is total black except worms that are in weird color, i can't see the terrain. What's wrong, I'v re-installed WWP and I have DirectX, and I have good graphics card and my computer is fast enough.

I tried to re-install graphic drivers, still doesn't work.

Check if you have any programs running that have an "always on top" feature enabled.
Like instant messengers, winamp, object desktop,...

Assuming you are using Windows XP: Have you tried running WWP in compatability mode for Windows 98 / ME?

I also set it to run in 256 colours only.

This seems to work for me with only the wormnet login password field being a funny colour.