TL;DR: Check your BIOS settings and run a live USB test to rule out Windows corruption before buying new parts. Just catching up on this. If the hardware checks don't lead anywhere, check the BIOS power settings. Sometimes a weird voltage setting for your Intel Core i7-11700K can cause a quick trip if the board is trying to boost too hard before it's ready. You could try resetting your CMOS by pulling the battery for a minute. Also, grab a bootable USB with Linux on it just to see if the system stays on. If it stays running in a live environment, your hardware is likely fine and it is just a driver or OS file conflict. If it crashes there too, check if your RAM sticks are seated right. Sometimes I see people have issues if they are using something like Corsair Vengeance LPX 16GB 3200MHz and the XMP profile is slightly unstable after a BIOS update. Use a tool like MemTest86 to be sure.

Here are some potential causes and troubleshooting steps that might help you diagnose and resolve the problem:

Potential Causes

1. Power Supply Unit (PSU) Issues: A failing or insufficient power supply could cause your PC to shut down unexpectedly.
2. Overheating: If the CPU or another critical component is overheating, the system may shut down to prevent damage.
3. Faulty Hardware: A malfunctioning component such as RAM, graphics card, or motherboard could be the culprit.
4. Software Issues: Corrupt system files or a problematic driver could also cause the system to shut down.

Troubleshooting Steps

1. Check Power Supply Unit (PSU)

• Inspect Connections: Ensure all power connections are secure.
• Test with a Different PSU: If possible, try using a different power supply to see if the issue persists.

2. Monitor Temperatures

• BIOS/UEFI: Enter the BIOS/UEFI setup during startup and check the temperature readings.
• Thermal Paste: Ensure that the thermal paste between the CPU and the heatsink is applied correctly and hasn't dried out.

3. Check for Hardware Issues

• RAM: Reseat the RAM sticks and test each one individually to rule out faulty memory.
• Graphics Card: Ensure the graphics card is seated properly and test with a different GPU if available.
• Motherboard: Look for any visible signs of damage or burnt components.

4. Software and System Files

• Safe Mode: Try booting into Safe Mode to see if the issue persists. If it doesn't, the problem may be software-related.
• System File Check: Use the sfc /scannow command in the Command Prompt to check for and repair corrupted system files.
• Event Viewer: Check the Windows Event Viewer for any error messages or warnings that might provide more information.

5. Other Checks

• CMOS Battery: A failing CMOS battery can cause startup issues. Replace the CMOS battery if it’s old.
• External Devices: Disconnect all non-essential external devices to rule out peripheral issues.

Next Steps

1. Replace PSU: If you suspect the PSU is the issue and have a spare, try using a different one.
2. Clean and Reseat Components: Clean dust from components and ensure all are securely seated.
3. Professional Help: If you’re unable to diagnose the issue, consider taking your PC to a professional technician.