Error while running query statment in oracle

I am getting this error while running query at sql prompt. not sure the problem.
could you please suggest me what to do and how to solve.

select i.issue_id
*
ERROR at line 1:
ORA-03113: end-of-file on communication channel



if i enter again into sqlpromt i can able to describe statement and run other sql statment but not the statement that cause this problem..

any suggestions please. its quite urgent.

thanks in advance

Your connection got lost.

Any other error comes along with ORA-3113?
Any trace file on your user_dump_dest directory?

The Connection To Database Are Lost

Check If Database Is Up
Check If Listener Is Up

And After Reconnect And Reexecute The Sql Query