Did you get to check your alert logs. Mostly the cause of the problems are written in the alert log file. So, could you check that and let e know of what you see in there at the time you had invoked your sql. Check whether the listeners are running, through "lsnrctl service" if not start your listener. Then check the service name had been defined in the tnsnames.ora file. If not create a service name for your instance. and try.

When you say memory fault, oracle would also note this error on its alert log through some ORA-#. If you could check that and find one, then it would be more easier to troble shoot from that point. At this point it is unclear whether it had been caused by the system or the oracle.

Sam