You will be stuck in fastboot if you have failed to flash an img file. You will have to boot a boot.img file using fastboot then download the last update to get your tablet back to normal.
Download the following file onto your computer...
Then unzip on the computer. You will see a file named "boot.img". Make sure your tablet is connected to the computer and you have the fastboot binary. Then run the following command in the directory you just unzipped the file
fastboot boot boot.img
This will allow you to boot up your tablet but the bootloader will STILL be stuck in fastboot. Therefore you will have to update your system. Download the same file above into the Download directory of your tablet. Rename it to update.zip. Dowload the following XML file...
and rename it to update.xml (NOTE: the system file manager won't let you change the extension so just rename to "update". Power off the tablet. Then hold down the Volume + key and hold down power button until it comes on. That will boot the system into recovery and install the update. In a few minutes you will be restored and your tablet will work normally. NOTE: YOU MAY LOSE YOUR DATA and may have to reinstall your apps.
If your boot partition isn't a mess like mine was, you may be able to just flash the system partition from the above zip file by using...
fastboot flash system system.img
The key is that a fastboot flash must be successful in order for your device to boot normally.