Rex rs 450 won't start, what could be the cause?

Hello dear questioners,

I recently bought a rex rs 450 with 1833 km privately

after a longer period of inactivity (4 years) the battery was defective

Now I have installed a new battery.

The engine now turns but still does not start

It is important to mention that I have two CDIs and when I try to start one of them the battery fuse immediately blows

What could be the reason for this?

How do I get my scooter started again?

I ask for help!!!!!!!!!!!

mfg