BB Bold :: Screen Goes Black And Freezes On 9900?

Recently after updating my bb bold 9900 to os 7.1, my device would start to give blank black screens even though the phone is on and supposedly working, since the keyboards would light up. At first it didn't do this, however, it has been around 10 days since it started blanking out. It would take around 15 minutes or more before I can see the normal screen again. I thought it was just a normal "blackout" since some time it tends to do that, but it turned out it wasn't. Sometimes when I use it, it would also blank out, which is annoying especially when I'm using the messenger/texting..