I have flashed modded bios through EEP programmer and inserted Chip back to the motherboard but the motherboard isn't booting!!
Now I re flashed original bios to the Chip and tested but same result..motherboard fails to boot!!

What may be the reason??

Hi Fernando,

But I have flashed latest bios through normal procedure and there wasn't any modification done to the same. so I was modified the flashed version (the same version I have flashed) and then re-flashed using EEPROM programmer (the normal procedures failed due to the security check) then try to start it isn't booting at all...

Check your chip to be a) inserted properly with respect to orientation, b) readable by programmer and c) has the same data read and data written.

Yes the orientation is correct & inserted correctly also double checked verified the data is available but still no success...I have another same motherboard with me so is it ok if I insert chip from that to this one for testing?? or will it affect both motherboards??

Well it seems the BIOS chip issue...I replaced chip from another motherboard and the board is working fine!! ....but I don't understand what may be the issue as the BIOS chip is reading by EEP programmer (miniPro TL866) and I am able to wipe it and re-flash it with master BIOS. but still no boot it stuck on CPU_LED and not posting at all.

I personally try not to mess with the original BIOS; just buy the same model of chip, backup the original chip and restore to new chip and then play with that. This way you can easily go back to original e.g. for warranty purposes.

It also reduces mechanical stress on the pins, e.g. if you have to remove/insert into socket a few times - you can by accident bend/break a leg and then - pain!

Try to buy a replacement chip and flash with the backup of the other chip that does boot, see if that works. Otherwise try another programmer? Worst-case perhaps one of the BIOS replacement services can make one for your mainboard for a bit more money.

Excellent...the only thing left was to flash original bios to the corrupted chip.. when you mentioned the issue then I extracted bios from working chip and flashed it to the corrupted chip and inserted back to motherboard..and it is posting!!! the main thing I failed to understand previously I was trying to flash latest BIOS which is downloaded from ASUS website only..but it was not working...this issues are never with Gigabyte BIOS chips...I am first time using ASUS BIOS so I totally confused with the behaviour...can any one tell what may be the real factor behind this??

Sure. ASUS files have UEFI capsule header, and if you haven't removed it, than you wrote the header too and such broken binary will never work.

@CodeRush

Thank you, you are a master in UEFI BIOS I know...but I flashed original/un modified BIOS to the chip but still it was not booting....also is there any way we can remove this UEFI capsule header??
Also if I need to modify this BIOS then should I copy the backup BIOS from chip and modify it??