Stereo Advice Needed

[JP ONeill]

So, I bought a 2004 A3 Special Edition, and the stereo doesn't work. I ordered some keys from eBay and took it out. The previous owner had an aftermarket stereo in and must have took that out and just put the Concert back in the slot. I reconnected all the cables, but it would not turn on. Am I missing something? The fuse box loks a bit sparse, although this model is quite low spec. 

Does anyone know if there is a cable or fuse missing? The fuse in the back of the stereo hasn't blown. 

Sorry, I'm something of a novice when it comes to this stuff, but don'want to fork over £30+ to a mechanic to fix it. I have a Sendai stereo but fitting that would require cables, face plate etc and cba lol

[big al 83]

Does it come on at all. If it does then you may need a code.

[JP ONeill]

Nope, doesn't power up

[cliffcoggin]

Is there a fuse in the box, and is it blown?

https://www.google.co.uk/search?q=audi+a3+fuse+box+diagram&newwindow=1&rlz=1CAACAH_enGB721GB721&tbm=isch&source=iu&ictx=1&fir=VP6je8ENromZAM%3A%2ChL0vLgAqNI2eNM%2C_&usg=__tYY2oOx-nFVJSuk3v4K3oMNP3pU%3D&sa=X&ved=0ahUKEwiRvdq89fDYAhUmJMAKHe_fAvQQ9QEIKzAA#imgrc=_