Windows Defender: Application failed to initialize

Problem Description
Customer's computer plagued by several strange errors.  Couldn't print, Webroot Spy Sweeper wouldn't work, Trend Micro AntiVirus wouldn't start, and Windows Defender failed to start.

Solution
After further troubleshooting, went into Services and found that many services were mysteriously disabled.  By sorting by Startup Type and comparing the disabled items with this list, was able to re-enable the disabled services.