I'm going to make an assumption, please tell me if I am wrong. Your old computer is an SGI or other, that outputs the video signal on a 13W3 connector, where both the horizontal and the vertical sync signals ride along on the green color signal. Your monitor doesn't do sync on green, being a standard "PC" type monitor with a VGA D-15 connector on the back, so you need an adapter that takes the combined horizontal and vertical sync signals off the green signal and splits them out to separate horizontal and vertical signals. I use an adapter cable that is male 13W3 to female D-15 (if you can only find a cable terminating in a male D-15 then you will also need a gender changer which is two female d-15s back-to-back) going into a SOG to VGA converter (I do not know if the rules of this forum will allow me to mention a commercial product but in any case I have no connection to the company I have in mind except for a single purchase three years ago) going into a standard VGA cable with male D-15 on both ends. The setup seems to work pretty good.