ACPI or why the OS does not boot?

Question

linux

I took a server for experiments on hetzner. (EX5 Intel® Core™ i7-920). Installed Ubuntu 12.04 on it (provided by hetzner). XEN rolled on top of him.
And the server stopped rebooting normally. That is, the commands - reboot, shutdown -r now - cause the server to freeze tightly.
The "WOL" and "Execute a automatic hardware reset" commands do not lead to a positive result (the server is not available).
Raise the server is obtained only through a request to the support service.
Moreover, they write that the server crashed due to an ACPI implementation error in the kernel, and advise using the “acpi=ht” parameter in the bootloader.
After the first time, I did just that. But subsequent reboots followed the same scenario.

Dear Client,
as requested we have restarted your server. It was hung on reboot because of a
faulty ACPI implementation in the kernel.
This can be fixed by adding "acpi=ht" to your default boot entry. After the next
reboot this should not happen anymore.
alternatively, the server can be shut down and then restarted using WOL via Robot.

only found in dmesg so far

drm: registered panic notifier

Are there any options for solving the problem, otherwise, somehow waiting for 1-2 hours until support starts the server is not interesting.
Can eat OS for XEN with normal implementation of ACPI? (the choice of ubuntu is purely subjective)

Answer 1

Look at other OS ?
ArchLinux
Fedora
OpenSuse

Answer 2

We use Ubuntu in Hetzner, for a long time and a lot, there were no complaints.
I can advise you to upgrade, usually this helps:
sudo apt-get update
sudo apt-get upgrade