dual monitors

I have a problem of trying to connect dual monitors in my pc,my graphics card is a nvidia geforce gtx 260, so i used a dvi  to hdmi cable to connect to my first monitor and worked fine, and when i try to use a normal vga cable to connect to my other monitor which is a (sony klv-s23a10) it doesnt work/doesnt detect it, it doesnt show up when i click screen resolution on control panel, please help me fix this problem