My guess is that pierremcalpine is right (dead battery) or that you knocked something loose during the work you just did.

There are a gazillion threads on "no crank" but the things you want to look for initially...
1) A green "key" on your dash (indicating that there's a problem with the immobilizer circuit preventing the starter from engaging)
2) Make sure that all the leads going to your starter are intact. You can use a voltmeter or even just a test light to make sure that you have a solid 12 volts at the big red lead, and at the small red lead (both when the key is turned to start by someone else).
3) Put the voltmeter between the battery post (not the terminal clamped to it), and the other lead on the engine block (an unpainted bolt or other solid connection). With the key turned there should be almost zero volts (indicating that you have a solid connection). A loose ground connection will result in voltage across these two points, since the bad connection / cable is going to be "dropping voltage".

The quickest test of the electrical system that's acting like yours is to turn on the lights, and then hit the starter. If the lights stay bright but the starter doesn't engage, you know it's not the battery. If the lights dim, you know it is (or it's a bad connection / cable that connects the battery to the car).