Usb cannot recognized (by 2 users)

Reinstall your USB drivers:
Navigate to Device manager, find a branch named "USB Controllers" or similar
Right click the one thats the problem (or all of them if you dont know which), select Uninstall
Reboot your machine and windows will autodetect the USBs and reinstall their drivers

Check the BIOS and see if they are enabled...

Disable power management on the USB hub To preserve power, Microsoft Window XP tries to disable USB when a device is not used. Under certain circumstances this function does not work and may cause USB devices to fail to respond when called. To resolve this issue, disable power management on the USB hub by doing the following:

1. Click Start , and right-click My Computer .
2. Click Properties , then click Hardware .
3. Click Device Manager .
4. Double-click the Universal Serial Bus Controllers branch to expand it.
5. Right-click USB Root Hub , and then click Properties .
6. Click Power Management .
7. Deselect Allow the computer to turn off this device to save power .
8. Repeat Steps 5 through 7 for each USB Root Hub.
9. Click OK , and close Device Manager .