Hi Everyone, We have a ZT-280, C-91 tablet. According to our tablet specs, we are running...Android version..2.3.4, Kernal version...2.6.34, cpu info...ARMv7. Our model#..zt280102c91m512f8. I went on the Zenithink website, and saw there was an upgrade version to 4.0. This said that it would work on all C-91's. So,I downloaded and unzipped it. Formatted my kingston 8 gb sdhc card, and added those files to the sd card. I held the camara button in while pressing the power button as per instructions. An unusual screen comes on, saying not to touch anything, as the screen is calibrating. Then it just boots into normal operating mode. Like it's not recognizing the sd card, or the files on it. Sorry, as I am very new to these tablets, and Android systems. Any help would be great! Thank you!