Yah, use boot -a -v.
It sounds like you simply have one of those systems which only works
without ACPI. It is likely, however, that only one or two of the ACPI
features are the cause of the failure. You can disable particular
ACPI functions at the boot prompt or in /boot/loader.conf. Quoting
from YONETANI Tomokazu:
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There's a kernel environment variable called debug.acpi.disabled, to
disable ACPI features. This helps narrowing down which part of ACPI code
is causing trouble. You can specify one or more of the following
separated by spaces.
acad bus button children cmbat cpu ec
isa lid pci pci_link sysresource thermal timer
"acpi" disables everything
"bus" disables "children"
"pci" disables "pci_link"
pci-related code in the acpi code in our tree is said to be incorrect,
so you may want to try disabling it first. There's also been a report
of lock-up which was worked around by disabling thermal code, but I'm
not sure whether it applies to your T42p.
------- end quote -----