Acer Nitro suddenly shutting down

I have an acer nitro 5 515-54. Its 4 years old and I really cant afford a new pc atm due to college. I tried fixing the bios, driver and updated everything. I replaced the fans and see if the power was connected. I went to an expert and they told me to replace the fans so i did. I really dont know what to do anymore. Im planning to reapply some thermal paste but other than that i need some help on this. Im super broke atm so i cant go to an expert again. Any suggestions for help