Failure of Task sequence during the PXE is very common and sometimes it is very difficult to know why is it failing until you get the smsts logs .There could be various reasons why the Task sequence is failing.If you try to look at the reports,you may not get exact reason for the failure .There are couple of solutions to get the smsts*. logs incase of task sequence failure .Some of them are given here.
1) you can add task sequence action to copy the logs to share location using cmd as given in http://eskonr.com/tag/copy-the-smsts-log-files-to-a-sharesccm-server-if-task-sequence-fails-in-deploying-os/
2)Manually getting the logs using F8 command.
After the Task sequence session starts,press F8 (you should have this F8 command enabled in Boot image),CMD will open with the default path like x:\windows
Usually the logs will the stored in X:\Windows\Temp\SMSTSLog or C:\SMSTSLog or C:\_SMSTaskSequence.To know more about the logs location depends on the task sequence actions where it is storing the logs http://eskonr.com/tag/different-locations-for-smsts-log-sccm-task-sequence/
Now i want to see the smsts.log which is present in x:\windows\temp\smstslog during PXEBoot.
In CM12,the default path after pressing F8 will be X:\sms\bin\X64 .
To load smsts.log,you will have to change the Dir .
Type cd X:\windows\temp\smstslog
You will be redirected to X:\windows\temp\smstslog ,just do notepad smsts.log,it will open the .log file in notepad which is not good to read /identify the errors.If you have included trace32 in boot image,you can use trace to view the log.
Lets move onto the next step by connecting the network share to copy the log files.
on the command prompt that you recently changed the DIR to X:\windows\temp\smstslog just type net use k: \\192.168.10.15\soft (Where IP address is the computer to store the logs on the network ,k: drive letter to map and soft is folder on the share to copy the log files) .
It prompt you for the use name and password. Provide user name(ex:eskonr\eswar) and password (which is invisible) where eswar is the username should have write permission to the above share and eskonr is a domian.when you enter the credentials,it gives you message connected successfully.
In the commnd prompt i.e X:\windows\temp\smstslog type copy smsts.log K: .you will see 1 file copied successfully.You can open the smsts.log with trace32.exe which you can get if you install SMS/SCCM tool kit from microsoft.