Corsair PSUs are good and reliable. I would look for the problem elsewhere.
1. Are the 24-pins and the 8-pins power connectors plugged in and well mated?
2. Do you have a good power outlet strip? Plug in the computer directly to the wall outlet to verify.
3. Is the heatsink installed well? No overtemp on the CPU? Check this with RealTemp. (If the CPU heats up beyond the design specs, it will shut off as a protective measure).