It appears that you have an overheating system. Things to consider.
Is the computer located where it is fully enclosed (bad airflow) or in a more open area (better airflow)? Don't put PCs inside of cabinets unless you want to slowly cook them.
Are all of your fans functioning? If not, replace them. This especially applies to the PSU fan.
Is the system full of dust/debris? If so, clean it out with a can of compressed air.
Are you using a quality PSU? You get what you pay for. If you are using a generic PSU that can't handle your system when under load, you need to replace the PSU with a stronger model (many recommendations in the forums on this one).
Are you overclocking anything? If so, stop until you stabilize the heat/airflow/potential PSU problem.
Does your case have good internal airflow? Look inside the case to make sure cables are not blocking your fans. If so, move them.
Check these out and you may be able to solve your issue with minimal cost and hassle. Good luck!