Fresh build you say?
Format disks and reinstall windows with minimum hardware. Being CPU, RAM,HDD,CDD,and do not add expansion cards yet. Once you install windows again (and the drivers
that come with the motherboard), start adding components one by one. Extra Hard Drive, sound card, Ethernet card if necessary,then the GPU.
For some reason the 7770 doesn't like being installed in a fresh build like that. Similar issues happened to me to an extent that my system got bricked. First I thought I had performed a bad driver
installation. Card was underperforming, audio lags timed with fps loss, resolution would get messed up, monitors native resolution was unavailable. I went to use driver sweeper, and after I was prompted to restart my computer the system was bricked and refused to boot into windows. Apparently driver sweeper swept more than it had to.
After reinstalling the way I explained above I had no problems whatsoever. I believe I might of had something to do with installing the motherboard chipset drivers, and IGP drivers on top of the settings the GPU had done on the clean install. Or maybe it wasn't that, I really do not know. Some sort of conflict I am sure of.
Anyway, give it a try.