Eddie266

hi everyone I'm 19 and I own a 2006 Audi A4 2.0t not the Quattro with 125,846 miles , I just finished relplacing the diverted valve yesterday that had caused a check engine light, but while I was doing that I also removed the battery just because I didn't want to break anything, long story short car no longer has check engine but the stereo no longer works it's the stock Audi symphony and it has no display not even safe mode, what can I do?