HP Proliant DL80 Gen9 cannot connect to iLO
Solution 1:
Can you ping and telnet that IP successfully on 80 or 443? if so then the problem is browser config prohibiting TLS version which you should be able to change.
Solution 2:
It's possible to configure iLO to use custom ports, shut down specific connections or filter by authorized list.
If you have no idea what the settings could be the easiest recovery is to reset iLO 4 to factory defaults via server setup:
From the System Utilities screen, select System Configuration > iLO 4 Configuration Utility > Set to factory defaults, and press Enter.
The iLO 4 Configuration Utility prompts you to select YES or NO.
Select YES, and press Enter.
When prompted to confirm the reset, press Enter.
iLO resets to the factory default settings. If you are managing iLO remotely, the remote console session is automatically ended.
Resume the boot process:
a. Optional: If you are managing iLO remotely, wait for the iLO reset to finish, and then start the iLO remote console.
The iLO 4 Configuration Utility screen is still open from the previous session.
b. Press Esc until the main menu is displayed.
c. Select Exit and Resume Boot in the main menu, and press Enter.
d. When prompted to confirm the request, press Enter to exit the screen and resume the boot process.
https://techlibrary.hpe.com/docs/iss/proliant_uefi/UEFI_TM_030617/s_reset_ilo_defaults.html
Without monitor and keyboard, you'd have to resort to scanning ports and finding access to some service to configure/reset the rest - have you tried SSH? If an authorized list is used you'd need to change your network address as well which could take days.