You can't boot an 8400 in AHCI mode.
You Must put the sata mode operation into Raid Autodetect ATA mode.
UNDER CMOS SETUP Change the
Drive Controller Configures the serial ATA controller's operating mode.
Identifies and defines the SATA controller settings for RAID.
You can set the SATA controller to RAID Autodetect/AHCI,
RAID Autodetect/ATA,
or RAID On
System Setup: Dell Dimension 8400 Systems ... - Documentation
You cannot move a drive from 745 or 780 into an 8400 or vice versa.
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You receive a Stop 0x0000007B error after you ... - Microsoft Support
After you move the Microsoft Windows XP system (boot) disk to a backup computer, you may receive the following Stop error when you try to start the Windows XP-based backup computer:
STOP: 0x0000007B (0xF890B524,0xC0000034,0x00000000,0x00000000)
INACCESSIBLE_BOOT_DEVICE
INACCESSIBLE_BOOT_DEVICE
