Q I need to install Xubuntu on to a computer with no DVD drive. I have copied the file xubuntu-7.04-alternate-i386.iso to my home directory then burned it to a CD using Xfburn. The CD however will not boot on either of my older computers. They do boot from CDs, in fact the Dapper install CD boots and so does the CentOS install CD - but not the Xubuntu one I just burned. I checked the MD5sum on the burned image, and on the file I put into my home directory and they are the same.
A There are a number of possible causes for this. Going for the low-hanging fruit first it could be that you have written the ISO image to the disc as a file instead of as an image. When you look at the content of the CD, do you see several files and directories or just one big file? If it is one file, you have not written it as an image. With Xfburn, you should use the Burn CD Image button. Another possible culprit is the disc. Are you using CD-RW discs? If so, try a new one, or a CD-R. CD-RW discs have a lower reflectivity, which becomes even worse when they have become scratched with use.
This can be compounded with older computers, where the drive lasers may be getting weaker and the lenses dirty. This may not be bad enough to stop your drive reading the disc, but it may slow down the process enough for the BIOS to decide there is no bootable CD in the drive and move on to the hard disk. One solution for discs that refuse to boot is to use Smart Boot Manager. Write the file to a floppy disc, boot from that with the CD in the drive, then choose the CD from the Smart Boot Manager menu.