No problem, SMC stands for the System Management Control - it controls electrical supply in the iMac as well as alot of other things - to reset it shut down your iMac, then remove disconnect anything else to the iMac - USB leads, mouse, printers etc. Remove the power cable from the back of the Imac.
Then wait for 15 seconds - then plug the power lead back into the iMac and attach all other leads again and start up. And thats it - hope this helps as this problem drove me crazy with the WD drive for over a week!
