My iMac suddenly takes a good 30 seconds to fall asleep after I tap the power button or select sleep from the Apple menu. It used to sleep after only 3-5 seconds, but now it takes much longer. The only major change I've made to the computer since this problem began is set it up at a different electrical outlet. I haven't changed the energy saver settings, no bluetooth connectivity, no change to network settings or hookup. Any help?