Something went sideways. The phone boots to a logo and stops, or it boots to recovery and gives you a wall of red text, or it does nothing at all. First move: put it down for sixty seconds. Adrenaline makes people reflash random zip files, and random zip files turn fixable problems into weekend problems.
Two kinds of broken
A soft brick means the phone still responds. It powers on, shows a logo, reaches the bootloader or recovery, and fails to boot Android. Wrong ROM, half-flashed image, a bad kernel, missing firmware blobs. Fixable in an evening, usually with the same tools that broke it.
A hard brick means no response at all. No logo, no LED, no charging icon, no `fastboot devices` output, nothing. Dead silicon. The distinction matters because the recovery paths diverge completely.
Recovery mode first
Force a restart: hold power for ten to fifteen seconds. Then catch the recovery combo on the way up. Pixel and most phones want power plus volume down for the bootloader and power plus volume up for recovery. Samsung wants power plus volume up plus Bixby on the older models. If TWRP or the stock recovery appears, you have options and the evening is salvageable.
Start with `Wipe, Dalvik/ART cache` and `Wipe cache partition`. That fixes a surprising share of bootloops after a dirty flash, and it deletes zero of your data. If the ROM zip is still on internal storage or an SD card, flash it again from recovery. With a PC nearby, `adb sideload lineage-21.zip` works from recovery even when the touch UI is dead. Sideload mode is the cockroach of Android. It survives things that kill everything else.
A bootloop right after a kernel flash is usually the kernel. Flash the old one back. Everyone skips that step exactly once.
Black screen after the logo? Leave it for ten minutes before deciding anything. First boot after a wipe takes up to fifteen minutes while ART compiles apps in the background. The people who panic at minute six and force a restart manufacture their own bootloops.
Fastboot next
If recovery is gone but the bootloader answers `fastboot devices`, you’re in the best shape of a bad day. Re-flash the partitions you touched: `fastboot flash boot boot.img`, `fastboot flash recovery twrp.img`, or on a Pixel, run `flash-all.sh` from the factory image and let it return the phone to stock wholesale. Check `fastboot getvar unlocked`. It should say yes. If it says no and the phone still won’t boot, the problem sits upstream of your ROM, probably in firmware you were told was optional.
Samsung devices get Download mode (power plus volume down plus Bixby on older models) and the Odin tool. Odin failing with `FAIL! (Auth)` means the firmware doesn’t match the model. `FAIL! (Size)` usually means a truncated download. Read the model number in Download mode, then re-fetch the file.
The deeper options
Qualcomm phones have EDL mode, emergency download, reachable with a test point on the motherboard or `adb reboot edl` on some devices. EDL talks to the chip below Android and below fastboot. It rescues phones that look completely dead, using the vendor’s own flashing tool and the right programmer (firehose) file for your exact chipset. Xiaomi’s MiFlash works this way. Finding that programmer file is the hard part, and the forums are the only source.
MediaTek devices get SP Flash Tool and a scatter file, same idea, different vocabulary.
When to stop poking
If the phone has been dead for three hours and you’ve flashed four different ROMs “just to try”, stop. The battery may be drained below the charging threshold, and a phone with a flat battery looks exactly like a brick. Put it on a wall charger for an hour before concluding anything.
Write down what you already tried. Filenames, error strings, which commands ran. Reflashing the same wrong file twice changes nothing, and every extra flash is another chance to interrupt a write and make things worse.
Two failed weekends in a row is the point where a repair shop with a box programmer costs less than your time. That’s information. Take it.