Can't Install ANY OS

So I picked up this 7-year old second hand computer, and I want to install Windows XP Home on it. It came with a version of Windows XP Pro with hundreds of user accounts that I did not have access to. Naturally, my first inclination was to do a fresh install of XP Home. I attempted to install XP Home, but some files did not transfer properly, and the OS would not boot after installation was complete. All of a sudden, NONE of my bootable disks are being recognized. My Ubuntu disk, XP Home disc, and XP Pro disc all throw the same error when inserted into the CD Drive upon boot: "Bootable Disc Does Not Exist", even though I have installed OSs from those EXACT same discs before...... No BIOS settings will help me

It's a 7 year old pc. Almost certainly a hardware problem. Time to troubleshoot. Resetting the bios is a good start. I'd then try a new dvd drive and running memtest86+.

Maybe you should consider removing data from older disk with FDISK from DOS and reFdisking and formating from DOS,I would never trust windoze in that regard,recommended boot order floppy,dvd/cd,hdd,under normal circumstances there is not usually media in either the floppy or the dvd/cd,so system will go directly to hdd,but if there is need for either floppy or dvd/cd then all you have to do is to provide same..