Update oracle table not responding -

i try update table sql developper request:

update cstm_t  set ten='new text'  dkey=<key>;

but when launch request, sql developper starts running request , keeps running.

when

select * cstm_t   dkey=<key>;

it's working , it's fast.

the same update java application has same problem. working before , updates on other tables working well.

thans help,

Trigger