Installed an aftermarket double din radio without disconnecting battery now my car will not start?

You must have bumped something; can you check the floormat to make sure it is not keeping the clutch pedal from being depressed completely? There is nothing from the radio that will keep the engine from cranking over, is the security light flashing? Here are the starter and radio wiring diagrams so you can see how the system works. Here is a guide as well to help test the starter trigger wire for power when in the crank position.

https://www.2carpros.com/articles/starter-not-working-repair

Check out the images (below). Please let us know what you find. We are interested to see what it is.