I'm trying to install RHEL7 on a Dell R210. The system was RHEL5, but had shred run against its disk. I tried booting a DVD with the RHEL7 installer, but got nothing, it would not boot. I've reburned the DVD twice with different burners, tried an old DVD with RHEL6 that has worked on other systems, redownloaded the iso and burned that, and even borrowed a USB drive, but nothing works. I've gone through the boot loader and made sure it is using the DVD, still to no avail. But the strangest part is that a CentOS7 and a Knoppix DVD work perfectly. It seems to be versions of RHEL that are the issue.
How can this be? What should I try?