@lsathya I really think there is something up/wrong with this hardware that causes iPXE to hang.
We do have a fall back method to get these computers to image without pxe booting. You will lose some capabilities, but you will be able to image them. Read through this article. https://forums.fogproject.org/topic/7727/building-usb-booting-fos-image Because of the way the forum works the first part is at the top of the thread and the subsequent parts are at the end of the thread. Read through the tutorial and understand what you need to do and the caveats by creating a USB Boot image for FOS Linux.
Also look in the FOG Forum chat bubble at the top for a few more hints.