Startup problems
Older Macbook Pro. Three beeps repeating. Mac fails to startup.
MacBook Pro 15", macOS 10.13
Question marked as
This would be RAM problem.
You do not say what exact Mac /model /year /size /retina /touchbar is this
or
what exact macOS you are currently running?
For example 2012 MBP...
Try re-seating the RAM: MacBook Pro: How to remove or install memory - Apple Support https://support.apple.com/en-us/HT201165
you are testing for both bad RAM or bad bank—
one stick at a time in each bank, If the RAM sticks prove to work individual—and banks work individually.
Other known issues are:
or
RAM banks slightly distorted/out of flat (use shims)