How do you troubleshoot SQL Server if its running very slow?

1]First check the processor and memory usage to see that processor is not above 80% utilization and memory not above 40-45% utilization then check the disk utilization using Performance Monitor.

2]Secondly, use SQL Profiler to check for the users and current SQL activities and jobs running which might be a problem.

3]Third would be to run UPDATE_STATISTICS command to update the indexes