I've seen this happen when the PXE services aren't really checking the DS database for active jobs.  When this happens, usually just restarting the PXE services seems to help.  If that doesn't help, then restarting the DS server will more than likely resolve the issue.

Please note that if you are attempting to use "initial deployment" and the machine is already in the database, it will not kick off any jobs from the initial deployment.  That is intended solely for machines that DS has never seen.

Try selecting the correct pxe menu option set in the job you are running.  If the job runs then the DS is not seeing that the computer has the job scheduled.  You may want to look at what your primary key is and verify that all the inventory has run on the computer.  That way the DS knows everything about the computer so it know that it is the correct computer to run for the job that is scheduled for it.

 OK to add:

it looks like it is automatically selecting the PXE boot environment (as it shows the "Altiris Auto PXE management ...." that shows up after it automatically selects the WinPE image).

But once it does that I get a:

PXE02: Exiting broadcomm PXE boot

and then the job fails.

This has never happened before, and I know it works on other PCs as I can push the image to a different PC and it would work fine.

I am going ot try another reboot in the meantime (once the WinPE image finishes rebuilding; my only theory so far).

Chris