upload bootloader to mega2560 using Uno

Run arduino ide (arduino 1.5.7 is required. won't work with older versions of software )
Connect the uno board to USB.
Open arduino ISP from examples.
Compile it and upload to uno board. (Board:Uno, Programmer Arduino as ISP)

Now make the following connections with the mega board. It is basically interfacing boards through SPI (MOSI, MISO, SCK) and SS(UNO) to RESET (MEGA2560)

UNO       MEGA2560
10 --------> 53
11 --------> 51
12 --------> 50
13 --------> 52

+5V --------> +5V
GND -------> GND

Select Board: Mega2560
Processor: 2560
Programmer: Arduino as ISP and then Tools > burn bootloader.Thsi time don't click upload.

Now connect mega2560 to PC and open a blink program. Compile and upload the program.