USB3 driver update froze, now PC does not boot (Windows 7)

[Neutrinos]

GA-Z97N WIFI MB
Core i5 4770K (I think)
16GB RAM
1 SATA SSD boot drive
3 SATA platter drives
GTX 930(?) PCI-E x16 graphics card
misc other bits

I tried to copy from an SD card reader so I could verify the functionality of a gopro I just bought. Win7Ultimate failed the USB3 driver update, so I began installing the driver from the setup files I downloaded from Gigabyte a few years ago (years? dang!). The installation froze my rig.

After a time, I powered it down, not expecting anything terrible. When I pushed the power button again, it makes no beeps but the water cooling system starts and the HD's make their noises. That's it. The monitor never gets a signal, even when connected directly to the MB.

I cleared the CMOS, both with a screwdriver (connecting the jumper pin-ups) and by removing the batt for 10 minutes). That didn't help. (Yes I unplugged it first.)

I've tried holding down, or tapping repeatedly, the F12, F8, F4, and DEL keys, but nothing happens (differing boot attempts). I never get to see the BIOS setup to change anything (though why anything should change is a mystery).

That rig was working fine this morning, now it won't even POST. Any ideas what can suddenly go so terribly wrong? No hardware has changed, but now it does not work a'tall. Essentially, I've created a large, liquid-cooled paperweight with a small blue LED on it.

 

[Sedivy]

Have you removed whatever was in the usb drives? Can you boot off of windows dvd/usb installation media?
But you should still be getting post for that. Can you open side of the case, look at your mobo manual and watch which light come on during boot sequence? (if your mobo has led diagnostic lights) Edit: and your small form factor mobo doesn't have any indicator lights according to your manual. Drat...
You have integrated graphics. Try pulling out the gpu and plugging the monitor directly into the mobo. Preferably dvi as hdmi can have issues.

 

[Neutrinos]

I unplugged the card reader; for some reason that seems to have helped. (Or it was disconnecting the batt for an hour.) Now it seems to boot fine, except now my keyboard and mouse (USB) do not work.

I'd already tried plugging the monitor into the MB. That didn't help.

But it ALMOST works now. My theory is that I have screwed the USB drivers and need to reinstall them. Using a non-USB keyboard and mouse. Thank Elvis this MB has PS/2 ports on it!

Thanks for your help!

 

[Sedivy]

Might not have been you but if you want latest gigabyte's drivers (earliest one that came on a disc might not have been the best option), get them from here:
http://www.gigabyte.us/Motherboard/GA-Z97N-WIFI-rev-10#support-dl