The battery could possibly need to be charged or changed all together. The display screen might be bad and the reason why the tablet will not turn on. If both battery and display are in working order, the tablet's motherboard should be replaced. When replacing or repairing the battery, display screen, or motherboard; refer to the following troubleshooting page for the ASUS MeMo pad. Asus MeMO Pad HD 7 Troubleshooting

The camera app may not be working. Also another reason for the camera not working is the presence of obstructions on the lens. Finally, the camera could possibly need to be replaced all together. If you are needing to replace the camera refer to the following troubleshooting guide for the ASUS MeMo pad. Asus MeMO Pad HD 7 Troubleshooting

The buttons get stuck by either having dirt in the button or because something is stuck behind the button. If you are needing a guide to cleaning or replacing buttons on your ASUS MeMo pad refer to the following troubleshooting guide. Asus MeMO Pad HD 7 Troubleshooting