2018 Macbook pro 15 inch won't boot up

Try running the Apple Diagnostics to see if any hardware issues are detected.

Try booting into Safe Mode to see if it will stay running.

You may need to try "Restoring" the firmware which resets the T2 security chip & firmware which erases the internal SSD destroying all data on the laptop. Then macOS must be reinstalled through Internet Recovery Mode. This "Restore" process requires access to another Mac running macOS 12.4+. If this "Restore" process fails, then the laptop will need to be repaired as it has a hardware issue.

FYI, it is always recommended to perform a clean install of macOS whenever acquiring a used Mac even if the previous owner has already done so. A clean install involves first erasing the whole physical SSD (Intel Macs only) before reinstalling macOS.

How to reinstall macOS - Apple Support

If you are able to return this laptop, then I would highly recommend to return it for a full refund while you can if you are still within any return period.

Follow these steps, testing after each step:

• Mac Startup Options.
• Mac Startup Methods.

If that didn’t help, then I recommend service.

Service Checklist:

• Mac service pricing.
• Check AppleCare Coverage.
• Get your Mac ready for service.

Click ▶︎ Start a Service Request. ⚛️

Need more help?

• Chat now or call 1-800-APLCARE.
• International Support.

Click ▶︎ Check Repair Status. 🔧

Dad2elm2 Said:

"2018 Macbook pro 15 inch won't boot up: [...]2018 Macbook pro 15 inch won't boot up[...]"

-------

Troubleshooting a Mac Stuck in a Boot Loop:

Is this consistent? If so, it seems you are in a boot loop. So, refer to the following...

I. Boot in Safe Mode:

In Safe Mode, Login Items do not run at login, certain preferences are set aside, and damaged system files are then reset. So, once booted in to Safe Mode, wait 30 seconds, and then boot up normally, attempting another update install. For instructions, go here: How to Use Safe Mode on your Mac - Apple Support

II. Reset your SMC and your NVRAM:

(Applies to Intel-Basel Macs Only) Sometimes changes (i.e. Installations) are made to the system and then settings (i.e. Networking) become corrupted, technically. So, reset both on your Mac. So, reset the SMC and reset the NVRAM or PRAM. It might take three tries. to fix this. So, be certain you have the time to do so.

Start With This:

• Reset NVRAM or PRAM on your Mac - Apple Support
• How to Reset the SMC of your Mac - Apple Support

III. Re-Mount the Drive:

Boot into Recovery Mode (Intel or Silicon) . You need to click the “Mount’ button to proceed. So, select the drives, and then click "Mount" Try rebooting once more. If of no success, then click unmount button, and then the mount button. Try rebooting once more. It looks dulled-out. So, if you cannot click it, then click the First Aid button to fix this volume.