PowerEdge R620 - Linux login problems

We have a Dell PowerEdge R620 with 10 cores and multiple terabyte harddrives, and we've run into a peculiar login problem with multiple flavours of Linux. The first installation was the latest Red Hat Enterprise Linux installation, and the second was Ubuntu 16.04, and in both instances, we ran into the same problem. After two or three logins, the server would no longer recognize the root password. In the case of the Red Hat Linux, the installation was from original Red Hat disks, and the Ubuntu version was installed from a disk created from the Ubuntu.com website. Nothing else was added to the system in either case, but once again, I am unable to login to the system. The keyboard and mouse are through a KVM that is connected to one other PowerEdge R620 and a PowerEdge R730, both running Windows Server 2012 R2, and there are no problems with either Windows machine. Additionally, none of these machines have yet been connected to the internet.

Any hints or help would be greatly appreciated,

Thanks,

Dan