I have flashed Hikey970 board with LeMaker Ubuntu OS. After completing the flashing process, when I boot the board, the monitor displays Input Signal Out of Range. Please kindly help me in solving the issue.
Maybe you can give more info so everyone else might able to help more.
I think that is not enough information. If you have completed flashing successfully in the right way, that cannot be happening unless there is problem on your source images.
Wild guess maybe maybe your monitor may not in the support screen resolution.
If it does not work, try also to switch your monitor to auto-detect, something that might work also.