I think this is the bug inside the 2.6.28 kernel.
You can try to use system rescue cd from
www.sysresccd.org/
I have forgetten the detail process when i using Fedora Core 6.
I many be wrong
1. craete a directory
2. Mount the file to that directory.
3. Find poweroff/halt
4. I odn't know whether user halt or poweroff.
I hope this helps.