Possible USB problems

For a while now ive had trouble connecting my MP3 upto my PC via USB. When attaching the device, which is meant to be plug and play, a small message box appears saying this device is not recognised. Following instructions that lead me through troubleshooting and to device manager, it says there are no problems.

I also tried attaching a IPod to the PC to the same effect. Currently the only device working through USB is my modem. Anybody have any ideas as to the cause of this?

Is it Windows XP?
If so, do you have sp1 or higher? That is required for USB2.0 drivers, but I'm not sure if that would be your problem. Always worth a shot.
Also you could try updating your USB drivers...If you don't know where to get them then tell us what model your usb card is, or what motherboard you have if it's onboard.