Used DELL OptiPlex 5040 SFF Motherboard T7D40 tested with I/O shield 818211801299 | eBay
A-Tech 4GB Module for Dell OptiPlex 5040 Small Form Factor Desktop & Workstation Motherboard Compatible DDR3/DDR3L PC3-12800 1600Mhz Memory Ram (ATMS283775B12046X1) at Amazon.com
Refurbished: Dell Optiplex 5040 Small Form Factor with Core i5-6500 3.20GHz Quad Core Processor, 4GB Memory, 1TB Hard Dirve, and Windows 10 Professional - Newegg.com