Arde,
I see you MSI KT4AV mobo has a Via Chipset, I've only seen this on nforce2 chipset boards but it may be worth a try....
Kareena,
Your ASUS A7N8Xboard has an nForce2 chipset. I had exaclty the same problem with my Biostar M7NCD with nForce2 chipset, also with Ath-XP 2600+.
I posted this earlier on linuxquestions.org....
I searched for ages for a solution, even tried a few other distros (gentoo, suse, PClinuxOS, Knoppix, Kanotix, even debian sarge and sid!), all would eventually start locking up, then only a hard reset was possible, which of course invoked a disk fschk and then HANG again!
What you need to do is include the following in your kernel boot options (append line in lilo) ..
noapic nolapic
note this isnt ACPI! it is the APIC which is interferring with the ACPI, or so I could figure out after loads of searching. I may have got the reason wrong but including the above options WORKS, I have not experienced a hang in over 2 weeks, including a spate of over 72 hrs without rebooting (yes I know its only a small amount of time but its just a figure, not a boast! lol)
And the second option above uses a lower case 'L' (not a number 1 or a pipe).
I use the above on any live CD i try, just pass those params to the kernel with any others, if its Grub then you can edit the line on the fly at boot time.
Also, if you use them with the boot options for install of MDK10.0 (mine used to freeze during install!!) then lilo will be configured with the noapic option, I always add the nolapic option to be sure.
Like I said above I'm not entirely sure of the reason, but my ACPI still works and power-down still works, and no hanging! I have no clue what APIC does, all I know it would screw my system! lol
Hope this works, and I have seen this for a few nforce2 boards.
Aus.