The failure of the hard disk to mount in this circumstance can be caused by a number of specific factors, such as the ROMs of the particular Macintosh computer being used and the system software version on the CD-ROM. In general, however, this occurs by pressing Command-Option-Shift-Delete longer than necessary. When held down for an extended time, these keys may be interpreted differently during startup, which can produce undesired effects such as the hard disk not mounting.
The timing of this key sequence is essential in properly mounting the disk drive. There is no need to keep the keys pressed once the "happy Macintosh" appears on the screen. At this point, the startup volume has already been chosen and continuing to keep the keys held down past this point may cause further undesired effects.
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