1. This could indicate a failing PSU that is not supplying power correctly to the motherboard. You may be able to get the PSU serviced but in most cases you will be better off getting a new power supply.
2. This could be due to overheating of the PSU or CPU: If the PSU is overheating, the metal cabinet may be hot to touch or you might get a shock. Shut off immediately. Check if the PSU fan is working, clean or replace the fan if not working or spinning very slowly. If it’s a faulty PSU you may be able to service it. If the PSU seems normal it might be due to an overheating CPU.