PXE Boot Operating System not found.

have you assigned a task sequence to the unknown computers collection?  did you create a boot disk for that task sequence?  can you take screen shots of the task sequence main properties pages so we can troubleshoot?

Yes you can see that on the Reference and Deployments tabs:

Thanks

a couple of silly questions... is the IP in the range you expected?  also have you set up IP helpers to point to the sccm server and if not have you at least set up option 66 and 67 in the dhcp server to point to the sccm server?

since you have assigned to unknown computers, and the pxe.log is showing no assigned task sequences.... that means the computer must be :"known"

look in your devices list for the device and also for devices call "unknown" - remove them - retry

Yes the Pool is:

and Options are:

for pxeboot.com it used to be :  SMSBoot\x64\wdsnbp.com , not sure which should I leave there

Unknown, if I understand it is not discovered by SCCM, usually applicable for baremetal.

The Task sequence is deployed to DC collection
you can see the DC collection, with computers that have installed OS, they are configured to boot from the Network in the BIOS
but they are not getting the task sequence from PXE.
I also deployed task sequence to a computer , not PXE  option,  just to show in the Software Center and that one worked...:

Probably the issue in the PXE set up.. let me know which information you need me to provide you in this regards.

Yes I did :

Thank you Guys!
I will setup the LAB later