If your Samsung Galaxy A55 is completely black and won't respond when you press the side button, don't panic just yet. The most common fix is incredibly simple and takes about ten seconds. Press and hold the Volume Down button and the Side button together for a full ten seconds, until you feel a vibration or see the Samsung logo appear on the screen.
This force restart is the equivalent of pulling the plug on a frozen computer. It clears out any temporary software glitch that's preventing the phone from booting up normally. I'd start with this every single time the phone seems dead.
Check Your Charger and Cable
Since Samsung doesn't include a charger in the box with the A55, a lot of people end up using old, underpowered chargers. If your battery is completely drained, a weak charger might not provide enough power to even show the charging icon.
For the best results, you need to use a proper 25W USB-C Power Delivery (PD) charger. Plug it into a wall outlet, not a computer or car port, and let the phone sit for at least 30 minutes. Look very closely at the screen in a dark room for any faint light or battery symbol.
Also, inspect the USB-C port on the bottom of your phone. The A55's port isn't as water-resistant as the flagship models, so pocket lint and debris can get packed in there, blocking the cable from making a good connection. Use a plastic toothpick or a can of compressed air to gently clean it out.
Boot Into Safe Mode
If the phone turns on but gets stuck on the Samsung logo or crashes during startup, a recently installed app is likely the culprit. You need to boot into Safe Mode, which temporarily disables all third-party apps.
First, force restart the phone using the Volume Down + Side button method. The moment you see the Samsung logo appear, immediately release the Side button but keep holding the Volume Down button. Keep holding it until you see "Safe Mode" in the bottom-left corner of the screen.
If the phone starts up successfully in Safe Mode, you've confirmed an app is causing the problem. Go to Settings > Apps, sort by "Last installed," and start uninstalling your most recent downloads one by one, restarting normally after each one to find the offender.
Clear the System Cache
Corrupted system cache files from an interrupted update or app install can also cause boot loops. Clearing this cache doesn't delete any of your personal data like photos or messages, it just removes temporary system files.
To do this, you need to enter the Android Recovery Menu. With the phone off, connect it to a computer with a USB-C cable. Then, press and hold the Volume Up and Side buttons together. When the blue "Installing system update" screen appears, release the Side button but keep holding Volume Up until the Recovery Menu loads.
Use the Volume Down button to highlight "Wipe cache partition," then press the Side button to select it. Confirm the action, then select "Reboot system now" when it's done. This process can resolve a lot of mysterious booting issues.
Consider a Factory Reset
If all else fails, a factory reset is your final software option. This will erase everything on your phone, all apps, accounts, photos, and settings, and return it to how it was when you first took it out of the box. You must have a backup in Samsung Cloud or on your computer before proceeding.
You initiate the reset from the same Recovery Menu. Navigate to "Wipe data/factory reset" using the volume keys and select it with the side button. You'll have to confirm this choice on the next screen. After the reset is complete, select "Reboot system now." The process will take several minutes as the phone sets itself back up.
Remember, the Galaxy A55 does not support wireless charging. If you're trying to revive a dead battery, you must use a USB-C cable. A consistent failure to power on after a factory reset typically points to a hardware issue, such as a failed battery, a damaged charging port, or a problem with the main board, which would require a professional repair.