Check if the button stuck In the device. Is tablet turned on? Does the button make clicking sound? If the button stuck inside the device, you'll need to take the back cover off and release it. If Button seems intact, but still doesn't react, you'll need to check the connection and make sure there is no damage to the button and area around it. when all else fails - you would need to replace the power button. Check out our Troubleshooting Page and replacement guides for more information.
First try rebooting your device, if sd card still doesn't show, pull it out and make sure it's going in the right way. It supposed to click into slot, otherwise you'd have to force it in, and it won't work. If it still doesn't show signs of life - pull it out, check the card slot on device with a light - make sure there are no signs of damage. If applicable - check sd card with another device to make sure card itself works. Refer to Troubleshooting Page for more solutions. Check out the disassemble guide to take the tablet apart and see if any damage not visible through the slot hole.