Put the j7 on a powered dock, confirm contact, then use the official reboot.
iRobot's j Series guidance says a robot with no lights should first be checked in the app, woken with its button, charged on the Home Base or Clean Base if the battery is dead, and rebooted if it remains unresponsive.
Find why the j7 will not wake up
Has the robot been sitting off the dock or with a very low battery?
A deeply discharged j7 can appear completely dead until it has time on a powered dock.
What to do when the Roomba j7 is completely unresponsive
Confirm the dock actually has power
Use a known-working wall outlet and make sure the dock cable is fully seated before diagnosing the robot.
Seat the robot correctly and allow battery recovery
Place the j7 squarely on the Home Base or Clean Base. If the battery is deeply discharged, give it time on the dock before expecting the light ring to respond.
Clean the charging contacts
With dock power disconnected, clean and dry the contact surfaces on both robot and base, reconnect power and dock the robot again.
Try to wake it with CLEAN
Press the single CLEAN button once. If the robot remains dark, continue to the reboot instead of repeatedly tapping buttons.
Reboot the j Series robot
With the robot off the dock, hold CLEAN for about 20 seconds, release it, and allow the reboot process to complete. iRobot notes that a reboot is safe and does not delete maps, schedules or preferences.
Do not factory reset as the first power fix
A reboot and a factory reset are not the same thing. iRobot says a reboot is safe and preserves data, while a factory reset deletes robot data. If the j7 still shows no response after verified charging and rebooting, contact support before using destructive reset steps or opening internal power electronics.
Use these guides if the robot shows some signs of life
Not Charging
Use this if the j7 wakes or shows lights but the battery percentage does not increase on the dock.
Stops During Cleaning
Use this if the robot powers on normally but becomes inactive partway through a mission.