Thank you :)
Hello,First of all sorry for late reply..Assuming you have kept the crystal connections as it is while uploading your program & settings as I told.I understand your problem, it seems that you did not edit or incorrectly edited "boards.txt" file.. because if you incorrectly edit the file, your program will get uploded but never run.Follow the "Step 5: Bootloading 2560. Part II"this may solve your problem :)
I got your problem..This device signature issue is not new..Can you tell me the exact number of your 2560 IClike for me it is "ATMEGA2560 16U-TW"The number after ATMEGA2560 if different, causes this issue..I'm soo sorry for late reply
Hello,go to Tools and in Boards option select ''Arduino Mega or mega 2560'' and again in tools select processor as ''Atmega 2560''. Now compile your code for Arduino Mega.