I have several memory sticks (thumb drives) that work flawlessly and several that won't show. These work in other computers but not on my computer. I have MAX computer with MSI 6728 mother board, Pentium 4 2.8 Ghz and 500 watt power supply.
As I changed the power supply from a 350 watt one to the 500 about 2-3 years ago, I wonder if the last power supply may be a factor in the response of the USB memory devices. Only one of my two mp3 players (m240 & m250) works on all USB ports consistently. The older one m240 works well. The m250 is iffy at times.