Before you use forceplan:
Check showplan output to determine whether index keys are used as expected.
Use dbcc traceon(302) to look for other optimization problems.
Run update statistics on the index.
Use update statistics to add statistics for search arguments on unindexed search clauses in the query, especially for search arguments that match minor keys in compound indexes.
If the query joins more than four tables, use set table count to see if it results in an improved join order.