Flashing? Do you mean it is loaded to the home screen, but blinking in and out? Or is it just stuck rebooting over and over?
If it is just not charging, then I would suggest trying a different cord to see if that works. Also try charging it through a different outlet.
If the device is under warranty, you may want to contact the manufacturer before doing anything. If it isn't under warranty, then first try pulling the battery, to get it to shut down (if it won't shut down by pushing the button). I know it can be a pain to get to the battery in tablets, so just be careful.
If that doesn't work, you may have to try and "Hard Reset" the device.
NOTE: Doing this will clear 'all' the data on your tablet, so it is suggested you not choose...