If I am reading your post correctly, you are getting the errors with Lubuntu from the installation medium? Did you do the usual md5checksum on the download? Posting some info on your hardware would be useful.
The CentOS installation medium is certainly not going to be looking for NTLDR and the most logical explanation for that is that it is not booting from the medium but the hard drive so I'm not sure what is happening if you have the boot priority set correctly.
You upgraded windows 7 to 8 and installed with MBR?
Have you disabled UEFI? I'm not sure if Win 8.1 will boot without it
OEM installs of windows 8 almost always are uefi. It can be MBR. I've read a number of posts on Ubuntu/windows 8 problems at Ubuntu forums recently and my understanding from the posts by their moderators is that both systems need to be the same, both uefi or both mbr. Otherwise problems result. I don't use uefi myself so have nothing to test on.