Radeon HD4200 and 5770 compatibility

I recently purchased a Radeon 5770 to boost gaming performance on my PC. The motherboard has a Radeon HD4200 IGP. When I install the the 5770 I get no output from either the 5770 or the 4200. It was suggested to me that I disable the onbaord 4200, however I have an old card that I usually use for it's svideo output and this works fine with the 4200. So I am asking do the 4200 and the 5770 work at the same time or will I need to disable the 4200 to use the 5770.

Thanks