Wierd problem with APC Back-UPS ES500
 

I have an old Dell Dimension XPST550 (Pentium III - 550Mhz. circa 1999) running as a small server. It is plugged into a APC Back-UPS ES550 so it doesn't reboot every time the power flickers (which is pretty often in this old house).

The UPS has a USB cable so you can monitor it. The problem I am having is if the machine does reboot it will no longer post with the USB cable plugged into it. Has anyone seen a problem like this before? It doesn't have an issues with my USB keyboard or mouse which are plugged into the same USB hub as the UPS. This isn't so much a linux problem as a general curiosity. I can communicate with the thing as long as I plug it in after bootup. I am in the process of trying to write some logging software specific to my needs.