Azureus does not start

From AzureusWiki

The newest version of NOD32 has no conflicts when combined with the latest Java. One possible cause is that you are running an old version of NOD32 Anti-Virus.

Although it is mentioned on Reduce CPU usage that NOD32 disabling Internet monitoring can reduce CPU usage, it is also the cause for Azureus not starting.

The javaw.exe must be added to the Internet Monitor exclusion list.

Procedure:

1. Click on the NOD32 icon in Windows notification area (tray).
2. Select IMON from the NOD32 Control Center.
3. On the Right side, click on Setup.
4. Select the Miscellaneous tab.
5. Click on the Edit button in the Exclusion section.
6. Click Add button.
7. Locate the javaw.exe and click Open
8. Press OK to close the Exclusion list.
9. Press OK to close the IMON Setup.
10. Minimize the NOD32 control center.

Start Azureus and it should start up.

Other reasons include:

Having a port which is out of range (Delete the Azureus.config file)

A rogue Azureus process running (Start>Run tskill Azureus)

Read the Azureus FAQ