PAGE_FAULT_IN_NON_PAGE_AREA AND MEMORY_MANAGEMENT

My desktop started throwing up an occasional Page Fault In Non Page Area BSOD. It accelerated to the point that it was happening daily then multiple times a day, with an occasional Memory Management BSOD. The system is now essentially useless; I can rarely get it to run for more than a minute or two.

I have run the windows diagnostic mdsched, plus I've booted to a Memtest USB drive and run the tests. Neither turned up anything, but I tried swapping memory anyway.
I also ran SFC/SCANNOW...

PAGE_FAULT_IN_NON_PAGE_AREA AND MEMORY_MANAGEMENT