Reinstall 12.04 LTS?

[Friggs]

I have already installed 12.04 LTS.

I would like to reinstall 12.04 LTS and clean out everything in my hard drive, but when I put in my CD and boot up I do not get the Installation screen but rather I get this screen prompting me to Login and enter a username. This login screen has no idea of my previous login credentials and also has these weird options like ubuntu and ubuntu 2D

So how can I get to that install and format screen like I originally did when I erased my windows XP and installed Ubuntu for the first time?

Thank you.

[Mr_JMM]

Just to clarify, you want to completely reinstall 12.04 to delete everything that already exists?

Can you confirm that the md5sum of the downloaded iso and on the DVD is correct?

Can you still login to the original 12.04 install?

Is BIOS set to boot from DVD before hard drive?