xHCI is USB 3.0 related.
AFAIK, if you delete any custom installed USB driver, windows should reinstall the default drivers from the built-in drivers of windows.
The weir part is that you told the the issue persist even after clean windows installation.
If the mouse, you claim that isn't working on the G551, works on other PC, only by "plug&play", i.e no manual driver installation is needed,
then I can only derive to the conclusion that your issue is HW based or bios / bios configuration based issue.
You said you've reflashed bios 207... have you tried 209 ? it was released not long ago 2016/04/01.
this might be a resolution.
Enter your bios and note your current configurations. ONLY THEN, perform the upgrade.
also, after the upgrade completed -> please enter the bios and "restore default" configuration-> save & reboot -> enter bios again and reconfig whatever you need ( like CSM, fast boot etc... ).
Also, as a compromise in the mean-time.... I've read that many users reports that if you plug a USB 2.0 HUB into USB 3.0 ports, and connect your USB 2.0 devices to that hub, their USB 2.0 connectivity issue solved ( this solved many the issue of USB 2.0 printers connectivity on win8.1 ).
Also, have you installed latest release of windows 8.1 or at least have you "windows update" your system to the latest update from MS ?
( EXCLUDING the KB3038853 or any other MS-bloat-ads-calling-for-win10-upgrade ) ?
Also, although my guide about USB 3.0 talks about using Asus's "USB 3.0 Boost" driver from the "Al Suite" package, it can indeed cause issues
according to some article.
Nontheless, I personally use it on my G751JT with win10 ( RTM and 1511 release ), and it works just great.
You need to rule-out that your issue is indeed not a SW for certain.
get ubuntu or windows on a USB / DVD , and try to boot them ( press ESC during POST, to boot from the external device ).
if you can't get it to boot on your laptop, but you can boot on other PC ( to rule out any mistakes during the USB/DVD creation ), it is probably HW issue and I advise you to RMA your laptop. ( I presume here, that the bios version change and/or re-configuration didn't help ).
Asus G751JTSamsung EVO 850 120GB + 1TB HDD 7200RPM
Cleaned installed Win 10 HOME
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