I've had similar problems as yours and as best I can tell it's an issue with poor quality ports on the case. Had two cases that were identical, and both of them exhibit the exactly same problem as you describe. One system I rebuilt just recycling the case, and the other I had some shop put together for me.
The two ports on the back of the system are connected directly to the motherboard. The two ports on the front are connected via a cable to the motherboard, and sometimes those parts are less than what you would consider quality.
Best thing to do, is just buy a USB hub or two and connect it to the back two ports, and forget the front two even exist.
First off, hi all 
Ok i'm running windows xp on a computer buit by a friend of a friend and its a little difficult to get him to fix the problem
I have a total of 4 USB ports, 2 back and 2 front. the back ones work fine, for example; I put in my memory stick, its recognised immediatley and I can use it. however if I try putting it, or any other USB device into the two front ports my computer recognises they are there, however it cannot access the device.
This seems very strange considering the device works in the back :S it seems stranger to that while the USB ports obviousley are plugged in and all, they cannot use any devices in there.
MY IT teacher suggested a lack of power to the devices. window hardware manager seems to suggest other-wise, or, in my ignorance i'm reading it wrong.Probably the latter.
oh, also my power supply has two inputs :s out of curiosity When would the other be used? could it solve my problem if the problem is power? or would i need a new set of independanty powerd usb ports?
Thanks in advance
Chowhound
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