Were there any messages printed during the reload? Specifically, watch for any messages during the time when the firewall is trying to load the 8.0(4) image. Those should give you a good place to start in troubleshooting this issue.
Unfortunately, I'm not sure how much help we will be able to provide then.
I would recommend checking the output of dir disk0: just to make sure that when you copied the image it saved successfully (and that it is named asa804-k8.bin). Other than that, your boot statement looks correct and it should simply be a matter of reloading the firewall to run the new code.
If the image is actually present on disk0 and named correctly, my best guess would be that the image is somehow corrupt and it could not be loaded when the firewall was booting. In that case, I would recommend simply downloading the image from cisco.com and loading it onto disk0: one more time.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...