The volume is at max and can't be decreased
seems like the volume up button always gives contact to put the sound at max. Sliding the volume down in dsi sound studio helps, but as soon as you release the slider the volume gets to max again.
Your "up" volume button is stuck down; check to see if any crumbs or dirt have gotten in there. You might need to replace the SD card slot and volume control assembly.
SD card receptor / Right and Left Shoulder Button Contact / Volume Control Buttons / Screen Adjustment Controls — Currently out of stock.