I'd try with default settings for clock and memory speed. If it still doesn't you go back to the shop where you bought the PC and let them fix it under warranty.
What happens if you reinstall the game from the original disk without any patches? It should work then.It's the first thing the shop will ask you: stock settings and a stock game to prove the machine is defective.
If you assembled it yourself ("tried to make" can be interpreted so) it's your own task to find out what's wrong.