What to do when your Samsung Galaxy 5S keeps restarting and custom os is taking too long?

[AC Question]

So yesterday my samsung galaxy 5s battery was at 0% and it was in charging. I was using it while it was in the charger and at 0%, then the screen starting showing like these colors as if water got in it or something, im not sure how to explain it, then after that, it just shut down. It started back up and said cannot connect to charger and i couldnt read the rest because it shut off within 10 seconds afterwards, and the thing is, it was in the charger. Then, it kept restarting. It kept getting on and shutting off. I tried to look for solutions and i did some kind of rebooting thing where you click volume up i think, home button, and power. Then some Warning thing came up and said click volume up to do something and down to restart the phone. So i pressed the volume down button and restarted it just in case but it still kept doing it. Then i tried it again, pressing all three buttons at once, and pressed volume up. It says downloading with that green android thingy. Its been going on for hours and im getting worried.
Someone please help!!
& it says dont turn off target but what will happen if i do turn it off?

 

[Rukbat]

Turn the phone off (take the battery out - that's the only way from the download screen). Hold the power button down for a couple of seconds to drain any remaining charge, then put the battery back in, plug in the charger and leave it alone for 24 hours.

In the future, don't let the battery get below 40% before charging it. A few drops to 0 like that and you'll need a new battery. (If you keep trying to get it to work the way it is, you might actually drain it down far enough to disconnect internally. Then it's trash and you have to replace it. [The reason for that is that charging a totally discharged lithium battery could result in an explosion. When they're made they have some charge in them.])