Have you been taking a lot of 1080p videos with the phone? Android phones take high bit-rate HD videos that can fill up the storage pretty quickly. If you can, go into your phone's storage settings and it should give a break down what is taking up the storage on your phone. I'd also recommend...
Does the led turn on when it's connected to a charger? Does it ring if you try to call it? It could be the digitizer has gone bad. You may need to replace the screen.
Any sd card from a well known brand should be good. Samsung, Sony, PNY and of course Sandisk. Personally, I use Sandisk sd cards for all of my mobile devices.