yum not working in centos5

[KernelMind]

yum is not working in my centos5, I am trying to install it but in the first step I found the following error:

[root@localhost yum]# wget http://mirror.centos.org/centos-5/5/...el5.2.i386.rpm
--14:27:44-- http://mirror.centos.org/centos-5/5/...el5.2.i386.rpm
Resolving mirror.centos.org... failed: Temporary failure in name resolution.

any idea?
thanks

[smolloy]

You're trying to install yum? Did you delete it?

[daark.child]

You shouldn't have to manually install yum on CentOS because its part of the base system, so should be already installed.

[KernelMind]

Thanks 'smolloy' & 'daark.child' for reply

I didn't delete yum...
but when I try to install any thing,e.g:
[root@localhost ~]# yum install zlib
Loading "installonlyn" plugin
Setting up Install Process
Setting up repositories
Could not retrieve mirrorlist http://mirrorlist.centos.org/?releas...86&repo=extras error was
[Errno 4] IOError: <urlopen error (-3, 'Temporary failure in name resolution')>
Error: Cannot find a valid baseurl for repo: extras

I found that error what can I do????

[daark.child]

Is your internect connection working properly? Is your machine behind a proxy? Try the following

yum --disablerepo=extras install zlib