Hi Brian, and welcome! We are generally a Linux support forum for PC's and servers, and Android is a little out of our realm, even though Android is based on Linux. There are many Android sites that may can help you better.
But I will offer a few comments as I have a little experience (very little!) with tablets and phones. What you describe is called a "boot loop". The tablet is stuck at boot up, and when it fails to boot it just tries again, over and over. You say you have left the tablet off for a period of hours... but if you can, I would suggest removing the battery and leaving it out for 2 or 3 hours. It probably doesn't need to be that long really, but removing the battery may help so that all the capacitors lose power and drain down their voltage. While the batter is out, you can try hitting the Power button a few times.... it won't turn on, of course, but hitting the button can help to discharge the capacitors more quickly if you don't want to wait for hours for a slow discharge. It still may not help though... it's just the easiest thing to do first.
If it is still stuck at boot, then next thing is to try to do the factory reset steps again. You probably did this with the system running before (choosing reset from the tablet's settings), and you obviously can't do that again... but there is a special way to turn on the tablet that can get you into a low-level menu that will allow a reset. These steps are described (with pictures)... check it out below. Be sure to begin with the tablet powered OFF.
http://www.hardreset.info/devices/dgm/dgm-t-909/hardreset/second-method/
There is a final way that is far too complicated for me to describe fully, but it requires finding a factory "image" of your tablet and "flashing" it to your tablet with special tools (Android SDK). I have not found a factory image that you can download, so this may not be an option anyway. The process is kind of like re-formatting a hard drive and re-installing an operating system... and it often causes boot loops when doing this too. If you think you will have to try this, definitely look around on Android forums for some more knowledgeable folks who may can help.
Good luck!