It is most likely the cpu fan that is blocked or no longer working. This fan is used to remove excess heat from the computer and if blocked can cause the computer to heat up and shut down. I would start by reviewing the [[ASUS X502CA Troubleshooting|troubleshooting]] page and the repair guide for the CPU fan. If the fan is clogged with dust just follow the guide to remove the fan and blow the dust out. If the fan is not working anymore then a replacement fan will be needed. The steps to replace are outlined in the fan repair guide.