Same here. I powered off the system hours after starting the installation. GUI just wouldn't come up.
After reboot the system does come back on.
Info Center
update: i was on v1.0 upgrade to 1.01 and now everything is working again.
I successfully upgraded xpenology DSM 5.2 to DSM 6.0.2-8451 Update 2 on my PC with B75MA-P45 (16Gb mem, 3x4Tb HDD).
But .... After the software upgrade, I kept getting an error message via http://find.synology.com/ (no HDD found).
Upgrade with the Synology Assistant, did the trick.