Windows 10: PC keeps restarting after powering on; No BSOD

Hello,I have this annoying issue where my PC Lenovo Yoga, Windows 11 keeps restarting after powering on. It happens every time, whether I intentionally shut the laptop off and power down, or if it goes to sleep. Each time I have to wait for the PC to restart. I am getting no BSOD which is making it hard for me to find help with my issue. This issue started after I sent my laptop in through Best Buy to get my cracked screen replaced, but I don't know why that would change anything I added the context here just in case.Things i have already tried:- disabling automatic restart.- updating window

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Random Restarts, No BSOD

He mentioned that he had done that above. Also I provided a BSOD details app. There were no BSODs to report.

 

PC reboots (no BSOD) on CPU stress

Hi fellow TPU members,

not too long ago, the box my gf's PC was transported in gave way on the stairs. Yes, you got it right, that sent a PC tumbling down a flight of steps alright.

Stuff broke. Also, stuff remained intact somehow.

I bought her a new case, new CPU cooler and we removed the floppy drive, so far so good. But the PC started crashing for no apparent reason, without a BSOD.

I tested:

• Memtest86+, left overnight, 0 errors
• Scanned the HDD for errors, nothing there
• Left FurMark burning up the GFX card and drawing some power, no problems there
• Ran Ubuntu from a Live CD doing nothing special, didn't crash
• Ran OCCT, Linpack, Prime95, all 3 caused reboots within minutes
• Oh, and I disabled "Restart on error" so I'm sure it's not a BSOD.

Now, I can still try and test something CPU intensive on Ubuntu, but my guess is the CPU didn't survive.
Before I do anything drastic like whippin' out the magic wallet and get her a new AMD quad, is there anything I didn't see?
I'm guessing the motherboard could be borkered as well, but can I check that other than replacing the CPU with a working one?
Any suggestions on which proggies I can use from an Ubuntu Live CD to stress the CPU?

 

Random restarts

when you start the computer up press F8 repeatedly until you get a list of how to start windows, choose do not automatically restart on system failure. if your getting bsod's list what your getting here so we can further help you. IF the system is not getting bsod's and still restarting as you say then i would look into getting a line conditioner for your computer as you might be having power issues.