Hmm, It sounds like I might've had this problem before, as my PC used to do this, and I replaced the PSU and it fixed itself, this could be something different for you.
This could be a RAM issue, PSU, a whole multitude of things, any more info you can give us, like what you were doing at the time when your PC shuts down?
Yeah that sucks man, if you want to check for yourself here's the link to the processor.
https://ark.intel.com/products/75105/Intel-Core-i3-4005U-Processor-3M-Cache-1-70-GHz-
It's really good, but if your looking to do OC'ing you may need to delid, getting a better cooler, or custom loop. But the temps that you have are good, as Ryzen can normally handle higher temps.
Make sure your cooler is dust free, and you may have to apply an undervolt especially if its turboing still, as this could cause easily higher temps, also consider upgrading your cooler.