I tried to sideload Android Pir onto my Oneplus 3 device . And I started rooting my phone. Suddenl5 the power went off and my pc got shut down. Then when I tried to restart my phone it's not starting.
If it takes Pie, it should be an a/b system. If you can find boot.img in the ROM image (that you download to flash to the phone), try booting with it using fastboot. (Start searching and learning - to get into the bootloader, to install the driver and adb/fastboot on your computer, etc.)