If you start your first generation iMac G5 computer in single-user mode, the computer fans will run at full speed for as long as you are in single-user mode. This is normal. However, on a first generation iMac G5 with Mac OS X 10.4.3 or later, the fans may continue to run at full speed even after you restart the computer normally.
If your iMac gets into into a state where the fans have remained at full speed after using single-user mode, follow these steps:
The fans should behave as expected after Mac OS X starts up.
This document will be updated as more information becomes available.