What you need in order to be able to boot from a CD (sort of checklist):
- a non-corrupt image (usual way of getting the contents to be burned on cd); usually can be verified by calculating md5sum, sha1sum or equivalent and matching it against the correct sum which should be (if exists) available where you downloaded the image from.
- a blank, preferably non-scratched cd to burn the image on.
- burn the image onto the disk using burn image
option, not as you would usually burn a data cd
. Most cd writing apps have a different tool/menu entry to burn images onto discs. Still I recommend downloading and installing a costless small app called ImgBurn, with which you simply can't fail - open the file, click burn, and it's done the right way.
- after the burn the disc should not contain a single file (the image file), but instead the contents
of the image file: usually some directories which in turn contain other files and maybe subdirectories, possibly further image files, ...
- BIOS settings should be set so that it tries to boot from CD before harddisks, or if you have a "boot menu" you can access with some key, use that to boot from the cd
That's about it. The part where most newcomers fail is the burning - some people just burn the image file as a regular data cd, end up with a disc filled with that single file (which doesn't do anything as such), and don't know why it won't boot. You can use your favourite image burning app if you don't feel like trying ImgBurn out, or don't have an easy-to-use Linux app to do it (like cdrecord), but just make sure you burn it right. If it won't boot after that, it's probably corrupted - but that's nowadays rare-ish with the "good modern technology", unless the image itself is corrupt already.
So: download the "right" checksum file from where you downloaded the image (MD5SUM or SHA1SUM or something), and use the appropriate tool to calculate a checksum from the image itself, and compare those. With md5sum it means: if you have downloaded MD5SUM file which contains the correct checksum, and placed it to the same directory where the image file is, cd there and run
and in a moment you're told if the image is ok or not. Or just run "md5sum imagefilename.iso" and compare the shortly produced longish line with the one at the MD5SUM file. The same procedure with SHA1SUM and equivalents, only the program/filenames (and checksums of course) differ.