Which version of SQL and which patch?
This sounds similar to my issue (which is posted in this section but has had no responses yet) where we added SQL 2008 R2 SP2 to a passive node (R2 RTM) and now SQL Service won't start when we attempt a failover. The SQL Log doesn't help because the failure occurs before the log starts writing, and all the Windows logs say is that the Cluster's start command times out.