Computer Restarts Itself

Hello,

I have a HP desktop computer. Whenever I'm just on Youtube or any website even Google, my computer suddenly restarts itself. When the screen comes back on it sometimes says, your computer shut it self down because it needed to protect the files.

But one other time it shut it self down and it said that a newly installed program was the blame for it.
I deleted my most recent one and I looked throughout my files to see if there was any programs I wasn't familiar with.

I don't think my computer restarted because it's getting overheated because this has happened before when I only used the computer like 5 minutes.

I'm not sure what's happening.

But the most common thing that is happening is that it's restarting. It never completely shuts down. The screens I usually get are the one that says open window with safe mode etc or just normally.

Thanks again, I hope this makes sense.