A few days ago a new ConfigMgr 2012 R2 OSD Hotfix is released. This because many customers couldn't PXE boot anymore. Have a look at these forums for more information about the issue:
Microsoft Technet, Windows Noob & MyITForum
This update resolves the following issues:
After you enable the PXE Service Point role on an instance of a specific distribution point, or you select the Deploy this boot image from the PXE-enabled distribution point property of a boot image, the Windows Deployment Service (WDS) stops running. Additionally, entries that resemble the following are logged in the Windows Application log:
Faulting application name: svchost.exe_WDSServer, version: 6.3.9600.16384, time stamp: 0x5215dfe3
Faulting module name: MSVCR100.dll, version: 10.0.40219.1, time stamp: 0x4d5f034a
Exception code: 0xc0000005
Fault offset: 0x000000000005f61a
Faulting process id: 0xae4
Faulting application start time: 0x01cec5d767184634
Faulting application path: C:\Windows\system32\svchost.exe
Faulting module path: C:\Program Files\Microsoft Configuration Manager\bin\x64\MSVCR100.dll
Note This problem affects only distribution points that are installed on site servers.
When operating system image files are downloaded to Configuration Manager 2012 R2 clients, you may find that the download takes longer than it did in previous versions of Configuration Manager 2012 clients. You may see this behavior when the target client is running Windows PE or a full Windows operating system.
You can download the Hotfix here: Microsoft Support