I have a CentOS 5 installation that has been working just fine for several months. Yesterday it became unresponsive - the screen remained blank - would not light up from mouse movement or keyboard and I could not connect to it by network.
With no apparent recourse, I finally held in the power button and shut it down. When I powered it back on it would fail the boot up:
...
Kernel panic - not syncing: Attempted to kill init!

The next thing I tried was to boot it to the install CDROM that I used when I installed it. This results in the message:
...
running install...
running /sbin/loader
install exited abnormally [0/0] -- received signal 11

...ultimately followed by

"you may safely reboot your system"

I'm thinking I probably have a hardware problem - maybe a bad memory; before tearing into it I thought I'd see if anyone might have seen this sort of thing before and have any ideas.

-Steve

signal 11 invalid memory reference

but the actual cause may be different.

Anyway check your h/w with a small live CD or USB distro

OK, - looks like it is memory - ran the memory test on the Centos install DVD -> lots of errors; removed 2 of the 4 Corsair memory sticks. Now it boots up OK.