Stupid question but is it because I need to put a graphics card in first as original cpu had vega graphics on it
That is not a stupid question, it is a very good and relevant question, and you actually solved your own problem.
If you do not have any kind of dedicated graphics card in your current setup, you will not be able to get a display signal to your monitor, since the ryzen 5 1600 doesn't have integrated graphics, which your previous CPU did.
So a dedicated grapihcs card is required in order to connect a monitor and recieve a display signal from the PC with the new CPU upgrade