I was in the process of cleaning and upgrading my old p4 pc. I removed the processor and CPU cooler. I then cleaned the thermal paste and reapplied a new coating. I re attached the CPU Cooler. How when I switch on the pc it starts to boot up and then shuts down after a few mins. If I restart a beeping noise comes from the machine and it might flash up on screen that the PC shut down due to a thermal event. Any suggestions
Seeing as you just did it, you might want to redo the sink/paste. You might have used to much/little paste and its now causing issues. I'd also double check that you plugged the CPU fan into the CPU fan header.