Today I had a strange problem.

I was testing OS deployment at a customer and had two test PC's that I was testing Windows 7 deployment on.

At first they could PXE boot and start the Windows 7 deployment but then deployment failed with an error.
I corrected the problem in the task Sequence and PXE booted again and this time the Windows 7 deployment was failing with a new error.

I corrected the error but now I could not PXE boot the computers anymore. When they entered the graphical part of WINPE they just rebooted again.
I checked the MSTSC log file that stated that "There is no task sequences available to this computer".
I checked the ConfigMgr console. Both computers (which was failing) was in the correct collection and they had the Deployment for the Windows 7 deployment.

I then google'ed the problem and found this where they have the same problem.

The problem turned out to be that the clients were not joined to the domain due to a wrong domain join password. So they were members of a workgroup instead.
But because the ConfigMgr client was installed but the computer was not members of the domain the ConfigMgr server would not approve the client. The default view in a collection in the ConfigMgr 2012 console will not show the "Approved" column. So I was not aware that the clients not were approved.

I added the Approved column and approved the clients and they were again able to PXE boot and install Windows 7.

Problem solved