My Win Xp PC can detect the sensor but shows that it is "not working properly". While the Spyder 4 Express software cannot read the sensor at all.
Anyone had similar problems before?
XP? Really time to retire. Have you checked that the USB port is working and giving enough power? Try using a unpowered HDD, if it works well then the power output should be fine.
The website states that Win XP 32/64bit is supported, but since this is an entirely different platform compared to Win7 I strongly suggest not betting on this backward compatibility.