Reboot enter the BIOS (message on screen "Press ??? to eneter setup" ??? could be Del, Esc, F2)
In BIOS look for an entry called Quick boot (or simular) and disable it.
Save and exit (F10)
What this does is force the PC to run all the checks prior to looking for the boot files on the hard disk, this delay allows the hard disk to get up to speed.