On some models of Mac desktop computers, the reset button no longer exists. They solely depend on a power button that sits on the front of the computer’s main unit. This affects, more particularly, the iMac and Mac Mini models. The Power Mac G5 fits in that list of computers, as well as later models in Macintosh’s line of products. If you want reset your Mac, just use the power button. Without a reset button or NMI (nonmaskable interrupt) button, you have little to choose from.
Save all the important work on your computer if your computer still responds.
Click on your “Apple” menu and click “Shut Down.” If your computer doesn’t respond, press and hold the power button for about 5 seconds until you see the screen turn off.
Press the power button again to turn it on again. You just reset your Mac desktop.