Racing Fans

Since yesterday the fans on my mid 2007 iMac have been running hard, specifically the fan dedicated to the processor.  What's weird is that the processor (or the HD for that matter) don't seem to be running hot but the CPU fan runs at almost 3,400 RPM constantly.  Here's a snapshot of my iStat widget (temps are in degrees F):
I haven't installed any software updates from Apple or any other software for that matter.  I've tried repairing permissions, resetting the SMC and PRAM, and letting the thing sit turned off for hours; whenever I start back up, the fans start racing after just a few minutes.
Any other suggestions?

I saw you reset the SMC however try again using the instructions below. You need to disconnect any peripharals. If that doesn't work then run Apple Hardware Test in Extended Mode, it's possible you have had a fan sensor fail. AHT is a lengthy test (30-60 minutes) and if it does not report an error the first time it should be run 2-3 additional times to be sure. It's time consuming but thorough.
SMC RESET
Shut down the computer.
Unplug the computer's power cord and all peripherals.
Press and hold the power button for 5 seconds.
Release the power button.
Attach the computers power cable.
Press the power button to turn on the computer.
PRAM RESET
Shut down the computer.
Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
Turn on the computer.
Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
Hold the keys down until the computer restarts and you hear the startup sound for the second time.
Release the keys.

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