itunes keeps checking library and wont load on imac
Is the library getting too big 461gb? This has been going on for a few weeks?
iMac Pro
Reboot your computer with the option not to reopen windows selected.
Press and hold down alt+cmd as you launch iTunes to open it in safe mode.
With luck it should complete a check of the library and save it properly so that iTunes can reopen normally in future.
tt2