Dell OptiPlex G1 - Manual (Page 6)

Power button Turns computer on and off.
Power indicator Lights up when the computer is on.
Reset button Initiates a hardware reset. To avoid possible data or file structure corruption, use
the reset button only when the system cannot be rebooted with the
<Ctrl><Alt><Del> key combination, and close any open application programs
or files if possible.
Hard-disk drive access indicator Lights up when the hard-disk drive is being accessed.
Diskette-drive access indicator Lights up when the diskette drive is being accessed.