Pls help me, i'm come from Viet Nam so i don't have condition to buy a new broad 
I made a arduino mega 2560, when i add firmware "C:\Program Files (x86)\Arduino\hardware\arduino\avr\firmwares\atmegaxxu2\Arduino-COMBINED-dfu-usbserial-atmega16u2-Mega2560-Rev3.hex" my PC display "Unknown device". I used ISP,
Lowvalue: FF
Highvalue: D9
Extvalue: F4
My PC running windows 7, but when i connected my board with mac, everything normal. So what happening?? @@ pls explain for me and how i can fix this
Thank you for attention! 