Check if you have specified cascade attribute. If it didn't work please send your code (tags are enough).

- Make sure you flush the session  or commit the transaction
- Make sure the cascade attribute of the association is set  to "save" or
"all", otherwise if you save  a Computer it won't save the dependent objects.
- If it's a bidirectional association, make sure you also set the other end
of the association (a setParentComputer in Hardware?).

one comment here:

CMT demarcation must be used by Entity EJB components

cascade is used for deleting complex relationships not for setting them

because you have a 1-> * relationship you need to consider to use a Composite Entity and define your Business Objects as POJOs, it's very difficult and error prone to have all Business Objects as Entity Beans and also it's not a good practice to do so

I'd say

1. Review how you have defined/designed your complex Entity relationship
2. Review the specification relative to your EJB version for transaction demarcation

but still have in mind

CMT demarcation must be used by Entity EJB components