No computer information to go by plus vague description of your problem with no supporting information concerning your issue.
How is your computer restarting or shutting down, like you pressed the computer case "Restart" or "On/Off" switch?
If that is the case that might be due to:
1- Overheating GPU or Processor
2-Overclocking
3-Power Issues (PSU) - weak or not powerful enough PSU or your PSU is defective.
Those three are the main reason for a computer to shut down by itself.
If the processor is overheating and shutting down what is your Make & Model of your processor that you have installed and what CPU Cooler you are using to cool your CPU?
If it is the GPU overheating, What is the Make & Model of your GPU card?
Need to know your Make & Model of your Motherboard, CPU, GPU, PSU, RAM Memory installed, and Windows, BIOS, and AMD driver version currently installed.
Install a Monitoring software and then Stress test your GPU and CPU and see if they are Overheating or if your PSU voltages are abnormal (past 5% of reference voltage).
You can use OCCT to check your CPU,GPU, & PSU or you can use Furmark's Fuzzy Donut to stress test your GPU card and see if it restarts while under stress. Keeping a very close eye on Temperatures and PSU outputs.
What exact errors are you getting before your computer crashes?
Any errors in Device Manager?
