Error occured when updating packages

when i check for upgrades i get this error message

W: GPG error: http://xnv4.xandros.com etch Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A3CCB76FA8BCF0C9

Before that I followed the instructions below to install the python IDLE

sudo bash
echo "deb http://xnv4.xandros.com/xs2.0/upkg-srv2 etch main contrib non-free" >> /etc/apt/sources.list
apt-get update
apt-get install idle-python2.5

now, when i select the install all upgrades option i get this error message

E:/var/cache/apt/archives/sysvinit-utils_2.86.ds1-38_i386.deb: trying to overwrite '/usr/share/man/man1/mesg.1.gz', which is also in package sysvutils

what should i do?

after that i was unable to shut down my computer, so i powered it off. now i cannot boot up xubuntu at all, after the it says starting up, i get the black screen of booting death.
i can access recovery mode but it stalls at
/bin/sh: can't access tty; job control turned off
(initramfs) [ 8.775041] Clocksource tsc unstable (delta = -740472046 ns)
[ 8.779054] Time: acpi_pm clocksource has been installed

is my computer dead?