Suddenly my PC shuts down and fails to power up.
I troubleshooted PSU (paper clip method) and it powers up fine. I tried to bridge the power supply pins on the board to make sure the cabinet power switch is not faulty and the system doesn't power up either. Is it broke?
paper clip does not always work to test the PSU. You need a tester that puts a load onto your power supply. I am a technician (12 years) and I have found the paperclip to be a good solution to see if the power supply with even spin a fan, but over the years I have found that its a bad way to test. Just an FYI. The CMOS trick might fix your issue though.