Can you try booting to the hardware test?
Hold the power button for 5 seconds, so it completely shuts off.
Then, press and release the power button, then immediately hold the D key.
It may do nothing different, but give it a minute to boot to the test.
If it does, run both the standard, and extended tests, which might take a long time (10 minutes or more) depending on how much memory is installed.
Do you know how old the MacBook Pro is?