Query does not complete

Problem:
The problem is an sql query that ran in Oracle 8.0.6 and took less than 30 minutes, does not run to completion under Oracle 8.1.7.2.

Hardware and Software:
The hardware is a 64-bit four processor IBM RS/6000 running AIX 4.3.2. The software running is Oracle Enterprise Edition Server 64-bit 8.1.7.2.0.

Work done:
I had the developer run the query. Opening up Oracle Enterprise Manager Console, I went into Tools | Diagnostic Pack | Top Sessions. In reading the Top Sessions window the query session in question registers Active for status and for the first ten minutes running the query “Session Logical Reads” counter increments. After ten minutes the “Session Logical Reads” stops incrementing and the status remains Active. We let the query run from noon until midnight, which is when the database shuts down for backup, the query results never returns.

Questions:
1) What queries, tools, or methods may I use to find why the query does not work?
2) I am new to Oracle Enterprise Manger Top Sessions. What exactly does “Session Logical Reads” measure? ( Number of Rows being retrieved? Blocks fetched? Bytes read?)
3) Are there other third party tools that may help in this situation, that Oracle Enterprise Manger does not do?