2008 Hyundai Sonata was running great turned it off now there is no power at all no lights or anything is there more than one main fuse

The 1st thing I would check is the battery to see if it has ANY voltage at all.
If it doesn't, the battery could have gone bad, the alternator is not charging the battery, or the drive belt that runs the alternator is loose or has broken.
Can the car be started with jumper cables from another vehicle?
If the battery has a charge, then inspect the battery terminals/ posts and cable ends that connect to the battery.
If they have deposits of white fluffy looking gunk on them, it is a safe bet that the battery is not making contact with the vehicles electrical system. You will have to have someone or yourself clean off that gunk.
There are inexpensive tools you can buy to do the job. You will need an appropriate size wrench to remove the terminals from the battery, and a battery post cleaning tool that has a wire brush for the battery posts (if the battery has them) and has a brush to clean the inside of the battery terminals (if you have that type).
I had a 1986 Chrysler Laser XT that the COMPUTER went bad on.
No power could get to the system to start, charge, or run.
Maybe that could also be the issue with your vehicle.
Good luck.

Your tests should start at the battery of course. Positive and negative with a meter. Your positive must be over 10.5v, and really over 11 to have more than 1 short chance at starting before it drains down.. If you have 11v+ positive, and your headlamps and brake lamps dont work at all. and ignition switch doesnt activate lamps on the dash or the radio, Id go to the main fuses underhood 1st, and also interior panel but do that one second. The primary fuses are a 100(ish) amp main in the underhood box, a 60 amp ignition,and possibly one labeled ALT or CHARGE that on some cars for practical purposes is the MAIN. And then many sub fuses underneath those in both boxes. It is rare to lose all fuses blow at once in either box, usually only possible if someone connected both battery terminals to jumper cables backwards. If that was done, start checking the fuses one at a time, and dont be shocked if 10+ major fuses are blown in each box (Or not). Easiest way to test a fise is touch a meter or grounded test lampo to one side of the fuse then the other, the meter should show voltage or the testlight should light on BOTH SIDES! If both sides are the same, the fuse isnt your problem. Some fuses wont show voltaghe because the circuit isnt on (headlamps or air conditioning).
Aside from that, if your battery has power and its not getting to the interior, your 1st checks are the above mentioned fuses, and 2nd would be ignition switched output, usually checked coming out of the ignition switch or at an ignition only power source like the lighter or the main relay.

First thing to check is the battery connections....make sure they are clean and tight. Try jump starting the car from a known good battery or another running car...not likely anything serious if it was running fine until you turned it off. If the alternator is bad and it killed the battery, you may have to let it charge for a while when jumping it.

Do a battery test, i found batteries can be a huge prblem. make sure it is tested. you can take it to your local parts store, autozone, napa and they can test it. also bad connections. with the cold and temp change in weather can make a bad connection.