PLEASE HELP: cant get arduino mega 2560 to dfu mode

hi newbie here!

ive been trying to update my mega's 16U2's firmware using Atmel's Flip and i'm stuck in the bringing to dfu mode stage - when i short ground and reset pins the arduino does disappear and then pops back as an arduino (not as an unknown device as should be) so i cant install Atmel's usb drivers.

the weird thing is that when i tried to do the same thing with my Uno R3 i wasnt facing any troubles.

i am using windows 7 x64 so if you can refer to some good pc tutorials i will be really happy

please help! i'm stuck on it for a week now and cant wait to start my project! thanks, tali

Why would you want to fiddle with the 16U2’s firmware?

When you short the pins and it shows up again as mega2560 then go to your Device Manager, then try the Update Driver Software. Then go to Browse my computer for driver software, and browse to the C:\PROGRAM FILES (x86)\Atmel\FLIP 3.4.7\USB folder.