You are using Centos 5 which is deprecated so nothing in yum will work until you follow this post to use the vault:
http://realtechtalk.com/Centos_59_Working_Vault_Repo_file-1921-articles
yum update
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* epel: fedora-archive.ip-connect.vn.ua
Traceback........
Upgrade Release Kernel TipsThis is for CentOS 3.1 to 3.8 but the methodology will apply everywhere.
I ran into a problem first of all with a non-booting system after running
#yum update centos-release
It took me to 3.8 and upgraded all the other packages [b:7e931c835d]BUT[/b:7e931c835d]
because of some stupid flags enabled in /etc/yum.conf the KERNEL WASN'T UPGRADED SO AFTER BOOTING, WELL IT DIDN'T BOOT OF COURSE :)
H........