After database restart all JBoss cached db connections are invalid ! Therefore you have to flush the database connection pool, that is 'internally' used by your CMP entity beans (most probably DefaultDS) via JMX console. Have a look at the "jboss.jca" service section to find the correct connection pool mbean entry.
Additionally you should also include an appropriate exception sorter entry in combination with a validconnectionsql entry into you datasource -ds.xml configuration, so JBoss removes dead connections from the pool by itself on SQL.
<new-connection-sql>set lock mode to wait</new-connection-sql>
<valid-connection-sql>set lock mode to wait</valid-connection-sql>
Did this fix work for you?