Try to clear the certificates from the browser, also try from a different PC and test w/ IE or Firefox, if none of this works you can try the Repair filesystem from the Extended tools in the Console screen (this will restart the system).
What is the build of DSSv6 that you are using now ? try a different build ( newer / older ) and try a different ISO file ( try to download a different ISO file and try to check it with .MD5 sum file to be sure that it's downloaded fine), and check the certificate, and create a new one if needed, for that, please check the following KB: http://kb.open-e.com/Create-a-new-certificate_148.html
If you are installing DSSv6 on a USB flash memory, then please be sure that you format it as FAT or FAT 32, and it's recommended if you used a flash memory with size of 1 or 2 GB.
Also try to run the DSSv6 you have on another machine ( for ex your laptop or personal PC ) and see if the GUI works or not.