Hi, my name is ***** ***** welcome to JustAnswer!
I'll be honest with you, this sounds like a motherboard problem. But let me ask some questions to make sure I understand the issue. When you say it cuts off and reboots, does it just spontaneously shut down, as if someone cut the power, or does it give you some kind of warning saying it's going to reboot?
Okay, can you tell me what kind of computer it is? And how long have you had this machine?
Also, when did this start happening? Did you make any changes to the computer between the last time it worked correctly and today?
That's fine. Can you answer the other questions for me?
Why kind of computer is it? When did this start happening? Did you make any changes around the time it started happening?
Are you still with me?