Graphics card connection to monitor

I installed a monitor formerly used with a dell C521.. worked very well for 7 years.. I bought a new Dell 660s and use it with that same old monitor.. works very well....I wanted to salvage some material from the old C521 and hooked it up to the same monitor that had worked so well for 7 years. Message on screen tells me that I have to" hook it up to a graphics card .".... as the connection that always did work, no longer allows for any function.... What's the answer?


Oneoldman