Guys, I need urgent help from you.

-- I have Western Digital Green Caviar HDD (model# wd15eads) 1.5TB.

-- Its been few months, it was running slow, when I try to access any data from it

-- When I tried to back up my data (all important), it failed.

-- I had some 150 GB of data on it, did not have any other backup

-- I have tried all possible ways to recover data (tried WD HDD utility, tried many data recovery software's) … no luck

-- Now it's not being detected by win7 or Linux,

-- Its detecting in BIOS, but showing "HDD: 4M - WDC ROM MOD"

-- I have very important data on it, can you please help me to recover?

-- if I get new HDD of same model n replace PCB (Logic Board) will it solve the problem

-- There is NO clicking or any other kind of sound from HDD. It is spinning properly.

Please help

No.
Most likely it's FW or head(s) problem. You will need a pro intervention in your present case.

Good luck.