Hi i just encountered the same problem with the zeki 8" TBDG874B.
what i did to get it of the flashy Android logo was hold down the volume button on the minus (-) side and get a small pin or needle to tap the reset. while holding the volume it will reset, then tap the power button still holding volume it will bring up a list. do a factory reset you lose all data but thats what i had to do. i tryed deleting the caches but didnt work. after the deletion select restart and the logo will again appear, just wait and it should come back to like when you first turned on and your golden, hopefuly. just dont do what you did b4 if anything. what i was doing was downloading a large file and was attemting to add an additional user at the same time
. sorry for bad grammer btw. hope this helps you or anyone else