Laptop restarts again and again

• If it restarts after running for a while, suspect heat. Clean the vents and use a cooling pad.
• Disable automatic restart on system failure in System Properties to see the error.
• Boot into Safe Mode (hold Shift while clicking Restart) and remove recent software.
• Run a malware scan.
• Check the RAM: remove one stick at a time if you have two.

A loop that begins at the logo needs a technician; back up your data first if you can.