Install hangs on Dell R510

Wanted to do a PoC with rockstor
Using Rockstor-3.8-13

Dell PowerEdge R510 with the latest firmware etc.
PERC H700 card with 8x 146GB SAS drives

Tried a CD-ROM, and several USB (and tested the USB on a pc, which works fine).

Tried troubleshooting - basic graphics mode. It gets to a black screen with a frozen mouse cursor.
Tried a 2nd identical Dell R510 server, same problem.

Tried reducing the RAM down to 8GB, same problem.

ideas? Appears to be a failure with x-windows on this particular hardware if I were to guess.