Hard reset to fix big problem on tablet?

[AC Question]

I recently received a tablet so that I can fix some videos on it which were unplayable, and after doing some research online on how to fix corrupted videos, I decided that it was probably not worth the time or money. Then I decided to see if I could find out what caused this problem so I started taking videos and pictures. When I started taking photos/videos all the photos/videos did not play either on the tablet or on my pc. However, after a soft reset it started to take photos/videos which were viewable. But later some disappeared and some became became unviewable by themselves. What is causing this problem? Should I recommend the owners try a hard reset to try and fix this?

The brand of the tablet is irulu model # is AX746
It runs android 4.2.2
Firmware version is v2.0