Switch traceflag 1222 on. That will result in a deadlock graph been written to the error log every time a deadlock occurs.
DBCC TRACEON(1222,-1)
Or, since you're on SQL 2008, check the extended events system health session
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability
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