Keyboard/mouse failure, Optiplex GX620 USFFV2

Howdy all, interesting thing here. About a month ago, one of your GX620's (ultra small form factor v2) stopped recognizing any USB mouse or keyboard. Figuring it was a bad USB controller on the system board, I ordered a new board. However, when the part arrived the next day, the machine was working perfectly again. Well, the problem is back. On boot, the machine goes through its normal routine, and after the DELL screen it shows the message "Keyboard Failure" as it goes through the next steps. Once at Windows, neither the keyboard nor the mouse work. No keys are stuck down anywhere, and I've tried different keyboards/mice to no avail. Just looking to see if anyone has another possible cause for the problem before I order me up a system board again. skemp