Yeh its RHEL 6.5 or RHEL 7.3 to be specific on Lenovo Thinkstation P520. I have changed it to legacy mode from UEFI and tried with these both OS which didn't worked out. I also tried a RHEL 5.2 version on it which followed the installation procedure but after rebooting showing Error 1962: No OS found.Can you elaborate which linux distro you want to install? 6.5 or 7.3 are not linux versions.