A good possibility is the thermal paste for the CPU to CPU cooler is compromised and needs replacing. May not be the problem but the first thing to try.   Take it to a repair shop.  
Everytime I start up my laptop, it starts getting louder and hotter within a few minutes and soon reaches 90 degrees. Playing video games is also impossible and it stops lagging for a few seconds when I unplug my charger but the battery is damaged. How do I fix this? I don't want to buy anything extra or open up the computer, I'm too scared I might break it while opening it.
Dell Inspiron 15 7577 overheats and then shuts down