sql agent job hangs without any errors or warnings
I have a similar problem in SQL Server 2008. We have hourly schedule which pulls data from multiple Sybase Adaptive and Sybase IQ servers and populates the SQL Server (Using System DSN, Linked Server). Every Friday after 2 AM those jobs hang. After a little bit of research on my Windows Server which has the SQL Server I found that the McAfee weekly schedule runs every Friday from 2 AM. 

As a short term solution, the anti virus scan can be cancelled and restart the SQL Server Service to clear the hang.

For long term, our security team has advised us to remove McAfee and load Kaspersky. 

A note here.. during the anti virus scan only those jobs hang which pulls data from Sybase (as mentioned above), all other jobs will run perfectly fine.