05hummer

Hi, I just had a AVIC D3 And a CDX P1280 Cd changer installed in my 05 hummer..First off when you hit the CD button you have to turn the volume all the way up to 40 just to here the cds(In the changer).. Second when I try to use my Onstar the unit turns off and nothing happens... Any ideas that may help me? thanks...Ward