The only thing i can think of right now is, whether the "cracked" gta-sa.exe is in the right place. Im assuming u have already done this, but i.ll still take a shot.
Before placing the No CD crack in the GTA folder, u need to remove the original gta-sa.exe from the GTA folder. And also, this often occur when u try to run the No CD crack directly from the desktop without having it placed in the GTA folder 1st.
Hope this makes sense.