Hy bro, if your pc is not turning on them there may be many problems other than one.
Like the thermogel has totally wornout, the BIOS of pc has some defect or improper setting, or your hard disk is corrupted or a simple problem, like the heat sink has gotten loose .
for your case i think your thermogel has worn out or the bios setting is not right
if the thermogel has wornout the just buy a new one(thermogel is a gel type substance used to help spreading out the cpu heat efficiently) wipe the old one and put new gel( just a drop of it and spread it similarly every where).
If BIOS setting is incorrect then when you turn the system on press F12 or F1 OR F2 , it depends on system, so just pree f12 and BIOS setting will appear then goto...