Did you in fact check the MD5 sums of the ISOs before you burned them (again)? That is what they are for-- to save you wasting CDs to burn "corrupted" files. If the MD5 of the ISO does not match the md5 file, don't burn the ISO-- just delete the file and redownload.
An alternative "fast and dirty" check under Windows is to try to open the ISO in a program such as WinISO or ISOBuster and see if it's readable by that program (if it won't open, then you can be pretty sure that the *.iso file is corrupt) and if it looks normal (does the Volume name appear, can you browse inside the folders, can you view a readme file, etc). This is not as absolutely reliable as an MD5 check (you won't be certain that the CD would successfully boot, for example), but for a fast and dirty check, it generally works.
IE is fairly well known for messing up downloads of this nature. I've not had problems using Mozilla/Firefox, but given that using a tool designed for the task you're trying to accomplish is usually the best choice when trouble strikes, using a dedicated FTP client is a good idea.
when I donwlaod no matter with smart FTP or WS-FTP , I can go up to 50% but no more, then it stucks.
Why linux mediacheck at the boot prompt, say that the ISO is corrupted?
If the download stalls at 50%, then is resumed, there's a fair chance that the ISOs got corrupted. No idea why that would happen unless your settings in the FTP client are not so good, or there's a problem with the mirror (which is odd for LinuxISO, but does happen).
Why don't you try a Red Hat mirror in your country
, or go to DistroWatch
and choose another distribution to try (the information page of every distribution they list contains a link to at least one download location if the distro is freely downloadable, plus lots more useful info about it-- and downloading a single-CD distro has got to be less frustrating than redownloading three CDs over and over)?
You might also try burning the CDs at a lower speed (40x or below)-- this sometimes solves such problems, because even media "rated" at 52x often does not perform reliably when actually burned at that speed. Also-- is the media you're burning to a CD-R or a CD-RW? Most Linux installers don't work well with CD-RWs, and using a CD-R is recommended.
Hope this helps.