CentOS 5.9 upgrade leaves systems unbootable.
Boot with a older kernel i.e. 2.6.18.308 and make a new initrd with the following command:
mkinitrd /boot/initrd-2.6.18-348.el5.img 2.6.18-348.el5 –preload hv_storvsc –p
reload hv_vmbus –preload hv_utils -f
Ref. https://www.centos.org/modules/newbb/print.php?form=1&topic_id=41048&forum=37&order=ASC&start=0