Wont start engine wont turn all lights come on and horn works what could be the problem?

Make sure the engine still will turn over by hand, then check the starter and make sure there is a good clean 12V connection from the battery and that the signal from the ignition switch is going to the starter.

I would return it to the installer

My 2012 Hyundai Elantra Wont Start - CarGurus

www.cargurus.com > Questions > Hyundai > Elantra

CarGurusJul 30, 2013 - My 2012 hyundai Elantra GLS would not start this morning. ... I hit my door unlock on mt Key fab and the doors unlocked fromt here I proceeded start my car.... it and it wont turn over just makes a light click. not like a battery issue. .... But if Istart from the zero position on the starter it doesn't start on the first try ...

No horn / No lights when I lock my car - Hyundai Genesis ...

www.gencoupe.com/.../244433-no-horn-no-lights-when-i-lock-my-car.h...

Mar 30, 2014 - 16 posts - ‎8 authors
I do not know what could have caused this but when i lock my car... ... lock yourdoors with your key fob(might have to hit the lock button twice) ... The alarm/horn should start beeping. ... 2010 Hyundai Genesis Coupe 2.0T R-spec in Karussel White.... My lights flash when I lock it, but the horn doesn't sound.

2013 Hyundai Elantra Engine Won't Turnover, Won't Start ...

www.carcomplaints.com/.../Elantra/.../engine_wont_turnover_wont_start...

The 2013 Hyundai Elantra has 19 complaints for engine won't turnover, won't ...

On some models you can disable the alarm after you connect the battery by locking and unlocking the driver door with the key.
I would disconnect the horn or pull the relay until you can get the alarm turned off.

I suggest you get one of those manuals people get nowadays to do it yourself..
My nephew use it to repair my car and it's totally repaired now.
you can get it from reliable-store or manualslife
also get instant help suggestions etc

What year is the vehicle ?

Does the engine "crank" over?
Are all the electrical accessories working, headlights, interior lights, horn, turn signals?
Let me know.
Regards,

Troubleshoot the starter. If your battery is good, then you WILL have power...the lights will work, horn, etc, but....if the starter is toast...you need a starter.

check you battery and battery cables...sounds like a big voltage drop