Keyboard and mouse don't work after BIOS update

We just got a new PC (Dell OptiPlex 7020) in which Device Manager says the drivers for the USB Controller are not installed (and its says "Code 28"). But the USB ports seem to work anyway (I have a keyboard and mouse plugged into them and they work). But I decided I should still  try to fix this problem, but was unable to. It keeps saying "Windows could not find driver software for your device."
     Then I noticed the BIOS was not current. So I updated the BIOS. Now when I boot up and get to the Ctrl+Alt+Del screen, the keyboard and mouse don't work; they're completely unresponsive. But they still work when I boot to "Safe Mode with Networking." I tried to undo the BIOS upgrade by removing the CMOS battery but I can't. The holder for that battery on the motherboard is designed to not let you remove the battery. In the BIOS settings I clicked the "Load Defaults" button, thinking that would undo it; it didn't.
     How I can get the keyboard and mouse to work again?
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The BIOS wouldn't get back to the old version anyway if you removed the CMOS battery. The battery only keeps the CMOS data, date and time, the BIOS is in an NVRAM chip which doesn't get erased if there is no power.

Since you can get into safe mode, try installing the chipset drivers for the PC.
john8217Author Commented:
When I go to Dell's site to see what chipset drivers are available, there are 2:
          -Intel Chipset Device Software Driver.
          -Intel Management Engine Components Installer Driver.
     Do you know which I should install?
The first one. It would also be a good idea to download and install all the other drivers after you have installed the chipset drivers and rebooted.

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john8217Author Commented:
I just realized there was a 3rd chipset option (I only saw 2 because I had entered the wrong OS in Dell's site). I ended up installing that 3rd one (Intel USB3.0 xHCI Driver).  I installed that one and it fixed the problem. Thank you for steering me in the right direction.
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