Help: Midi and audio both stopped

[zoid9]

This is on v3.75. (pre4.x works fine.)

Well, like the title says, it just stopped working. ASIO is set up the way I've always had it. Ditto for MIDI. I just cannot figure out why.
Most of the time I'm on pre4, but I come back to 3.75 when I want to use ReWire for Reason.
Never had any problem until today.
I uninstalled Reaper and took the REAPER folder out of App Data and did a virgin install. It still won't work.
I tried with ReSynth and got nothing. Same with ReaSamplomatic.
I've been working with Reaper long enough to know that NOTHING in my set-up has changed.
The only thing I can think of is the addition and removal of VSTs. But when I did the reinstall, no non-Reaper plugs were scanned.