My MacBook Pro screen cracked and can't connect to external display
Here is a slightly crazy idea to "give you eyes" on the Mac with the dead display. If you have easy access to a second Mac and the right cable to connect the two (e.g., Thunderbolt to Thunderbolt, USB-C to Thunderbolt, USB-C to USB-C, etc.), you could:


Connect the two Macs with said cable
Put your damaged MacBook Pro into Target Disk Mode by holding down its "T" key while you turn it on
Turn on the second Mac while holding down its Option key so you get to choose which partition to boot from
Choose the system volume of the broken MacBook Pro


This basically lets you use the intact second Mac to boot into the system that is installed on the MacBook Pro with the damaged screen. If there are indeed any software or hard drive issues with that first Mac that prevented you from logging in, you are now able to see and potentially address them.

For more details on Target Disk Mode, see this guide.