To turn on AMT:
I do not have a DELL 755 in my lab, but I found the User's Manual here.
You might also take a look in the BIOS screens and verify that AMT has not been disable from there as well.
I'm so sorry about that! I was at first thinking that the Dell 755 did not support AMT but when I looked it up on the Dell website, it appeared to support it. I'm glad you found Sree's blog, anyway.Apparently you aren't the first person to run into this issue.