MacBook Pro 2019 won't boot, fans pulse every 30 seconds

Make sure you are using the correct procedure for the SMC Reset since it has changed for the 2018+ Macs with the T2 security chip. Read the SMC article @WheelieNick provided.....you need to read the T2 section. I personally like to hold down the Option key immediately after the startup chime so the system is on, but not in any OS so when I perform the SMC Reset, the laptop will immediately power off so I know it was performed correctly.

If you don't know the password, then you won't be able to boot from a macOS USB installer since it would require you to authenticate with the T2 security chip in order to modify the security settings to allow booting from USB by using the Startup Security Utility (it is unlikely a company would enable this option for security reasons so booting from USB without knowing the password is impossible). This means you would need to perform a DFU firmware Restore to reset the T2 security chip which will erase the internal SSD. This will allow you to reinstall macOS through Internet Recovery Mode (even if the Mac is being managed by an MDM). However, at some point during system setup or use you may see a notification that the system is being managed (depends on how strict the company was with their management of devices whether you will see a notice during setup or some time later while using the computer).

How to revive or restore Mac firmware - Apple Support

If this doesn't help, then there is nothing else you can do. The Logic Board for the 2019 models have a much higher rate of failure than any other model (especially the 16" model, the other 2018 - 2020 models are not great either). You can try running the Apple Diagnostics to see if any hardware issues are detected. My guess is the battery was left completely discharged for a long time which permanently damaged the battery which is why the fan may be running at high speed. It may also be why you have issues booting the laptop since a power related issue can cause the USB-C Apple Intel laptops to run at very slow speeds.

I personally would not spend any money to repair any 2016-2020 Intel Mac with USB-C ports. A battery repair would be at least $250 US and you still have the issue of reinstalling macOS and a concern of whether this laptop may still be managed by the former employer. Plus these particular laptops have a lot of known issues. Plus since you cannot prove ownership to Apple's satisfaction, if the laptop has become locked (firmware password lock, or Activation Lock, etc.), there is no way for you to have Apple remove those locks. Is it worth the risk of spending money on repairs? I'm usually all for keeping equipment working for as long as possible, but I find it hard to justify spending money on these particular Macs even without all these unknowns.

Hi there

please try this

Check power connections

Make sure that your power cable is undamaged and plugged securely into your Mac and a working electrical outlet.

If your Mac has no built-in display, make sure that your external display is connected to power, connected to your Mac, and turned on.

Press and hold the power button

Press and hold the power button on your Mac for about 10 seconds. (Every Mac has a power button. On laptop computers that have Touch ID, press and hold Touch ID.)

Then press and release the power button normally.

Unplug accessories

You could have an issue with one or more accessories or their cables. Unplug all accessories from your Mac, including printers, drives, USB hubs, and mobile devices. Then repeat step 2, above.

If you see something on your screen

If your screen shows a flashing question mark, circle with a line through it, or anything else, your Mac is turned on but isn't starting up:

If your Mac turns on but doesn't start up all the way

If you see nothing on your screen

If your Mac seems to be turned on but the screen remains blank, the issue could be software related:

If your Mac starts up to a blank screen

Reset the SMC (Intel-based Mac only)

If you're using an older, Intel-based Mac, resetting the SMC might help:

Reset the SMC

If you need more help

If your Mac still doesn’t turn on, you might need service. Set up service.

A friend gave me her old macbook pro from her company that dissolved.

Therein lies a clue. If this is a "managed computer," that is, set up so only company IT personnel can make changes, then you may never get it to work, even if she remembers her password. We see a fair number of posts like this here where people buy or are given company computers that were not properly reset to accept a new owner. Only company IT people can reset the computer.

Does your friend remember if she had to rely on company IT reps for updates, or got updates only when company IT told her updates were available?