Windows 10: PC randomly reboots straight into windows lock screen

Hello, sometimes when I'm downloading something or opening a game, my pc will randomly reboot straight into the windows lock screen after about 20 seconds. I don't get a blue screen, I don't see the MSI startup screen where you can open bios, or windows logo. It just crashes to a black screen, then after about 10-20 seconds, I see the windows lock screen where I type in my pin to get to windows. If someone can please help me figure this out, I would really appreciate that. I will upload any dump files or anything like that that you may need to help me troubleshoot. Thank you very much i

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Computer Randomly locks up

Ok, so my dads pc (its in sp) completely randomly locks up.

Im not sure what the deal is.

it was working fine, i swapped boards and it game me a memory error but no big deal, fixed that. now, it locks up a few times a day, whether it is in the bios, or post screen, windows, trying to format windows ect.

Im not sure what to do! if its the board i'll rma it and give him "back" the P45 but if its ram or hdd idk...

what do you suggest?

 

PC Randomly Reboots

Just recently, my PC started to randomly reboot, to start it was once every other day, and know every few minutes.
Any suggestions to rectify this problem would be greatly appreciated.

 

PC Build Steps

Ok just because I like steps i am going to create some steps. Please give me the stamp of approval/disapproval

• Install system in case
  • Remember to connect SSD and optical to same SATA ports on motherboard
• Turn on PC
• setup HDD
• run blend test in prime95 for 30-60 min
  • run realtemp at the same time

• While in Prime95 test
  • if CPU goes above 70c in RealTemp, I have a leaky CPU
  • if my system locks up or blue screens, there is an instability in the system somewhere
  • if my system does not lock up or blue screen, my CPU is not damaged and I am in the clear!

What do you guys think??