Hi
When you see a question mark that means that the mac doesn’t know what to boot from(it also does this if there ISN’T anything to boot from)
If you haven’t reinstalled macOS you will need to do that to fix your issue
Here’s a guide in doing that
[link|https://support.apple.com/en-gb/guide/mac-help/mchl338cf9a8/mac|https://support.apple.com/en-gb/guide/mac-help/mchl338cf9a8/mac|new_window=true]
If you already have macOS installed I suggest you reseat the cable going to the SSD:-)
Hopefully this helps
Any questions please ask
Thanks:-)