Every once in a while with these tablets, the boot process won't seem to get past the initial stage, when the small, square Android icon is displayed in the middle of the screen. Sometimes I can get past this by holding Power + Up Volume during boot, which gets it into recovery, and from which I can choose to reboot the device, and then suddenly everything seems to be fine. But sometimes, such as right now, recovery won't come up while holding Power + Up Volume during boot, and the tablet sits at the initial screen forever. What's causing this, and is there a way to fix it?