I tried to disable the ACPI feature from BIOS, but it seems the machine enters a restart loop after I do that. It always restarts itself right before the system boot begins. Any ideas?
Are you using Windows, and are you getting to the part where Windows should start loading before the computer reboots?
Windows does not appreciate at all having ACPI yanked out from under it. There are different hardware abstraction layers (HAL) depending on whether your computer is single- or multi-processor, and whether it supports ACPI or not. If you install Windows on an ACPI-enabled machine, it will install the ACPI HAL. If you later disable ACPI, that HAL will not function properly.
From the Microsoft KB:
Microsoft does not recommend that you change the HAL that is installed during the Windows XP Setup process. When you change from the ACPI HAL to the Standard PC HAL, you must reinstall the operating system, and ACPI functionality is lost.
If you need to keep ACPI disabled, you'll need to use Windows Setup and choose the "repair installation" option. This will refit the operating system with the correct HAL for your current settings.
As others have asked, why are you trying to disable ACPI, anyway?