03/10 Update: the problems associated with KB4535996 are still increasing. The always diligent BetaNews, reports that some Windows 10 users who have installed the update are discovering that sleep no longer works correctly on their computers and Microsoft's KB4535996 community page is filled complaints including broken search, trouble opening apps and a growing number of users reporting their PCs will not boot after updating. Remarkably, three days on from these troubles beginning, Microsoft still states on its KB4535996 update page that it is "not currently aware of any issues with this update". Ignore this. If you haven't already, get the Windows Update troubleshooter and proactively block KB4535996. Until more is known, this is an update you need to avoid.

03/09 Update: Microsoft has confirmed Windows 10 has run into more trouble. The company has published a support page explaining that a new bug in Windows 10 can prevent users from manually installing drivers on their PCs. Users will receive the error message: "A driver can't load on this device" and it can break installations even after they appear to complete successfully. Microsoft states "If you choose to continue using your device without addressing the driver problem, you might discover that the functionality the driver supports does not work any longer, which could have consequences ranging from negligible to severe." Third party drivers can be essential, particularly for legacy devices, so Microsoft has offered a workaround which (perhaps surprisingly) involves turning off a Windows 10 security setting that guards memory integrity to allow the driver installation to complete:
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Are you booting up your Windows 10 machine and discovering you can’t log in to your profile? It appears you’re not alone. Reports are increasing across Twitter and Microsoft forums that following the most recent Patch Tuesday update (KB4532693), users are complaining that their profiles and desktop files are missing, and that custom icons and wallpaper have all been reset to their default state.

The generally accepted solution to this problem is browsing to the C:\Users folder with Explorer and checking for a folder named “.000” or “.bak.” Once you’ve tracked it down you can create a new Administrator account, log in to that account, then copy the folders and files back where they belong (Documents, Pictures, Music, Desktop, etc).
Bleeping Computer, however, is also reporting that several readers resolved the issue by rebooting “several times” or just uninstalling the troublesome KB4532693 update. The site also states Microsoft is aware of the issue and is investigating.