Take your mobo out of the case.
Remove the stock cooler and clean all the paste off of it. Do the same for the cpu.
Once both are clean ( look up how to do this if you are not sure) put the chip back in and re-install the cooler with new thermal paste. Make sure ALL four push pins are completely through the mobo properly. You could also look up videos/pictures of what it should look like.
With the board still out of the case, hook back up everything needed for the machine to post. Power the machine up and check your temps BIOS. If the temps are normal then the cooler is on properly and put everything back into the case.
Just make sure you keep yourself and the hw grounded so you don't fry anything.