Here is my complete arsenal of USB (Unreliable Serial Bus) solutions. Some you may have tried and some may not be relevant. Not in any particularly logical sequence, here they are:

1. Right-click My Computer > Properties > Hardware Tab > Device Manager to see if the drive shows up under ‘Disk drives‘. If so, right-click it > Properties > Policies Tab and check if you have a ‘Quick Removable’ check box. A USB external drive should have a check in this box. Reboot if you’ve changed anything.
2. Try restarting the computer with the USB drive already plugged in and powered up.
3. Try an ‘Autoplay’ repair, here http://www.microsoft.com/downloads/detai...amp;Hash=LJ6SCR
4. Right-click My Computer > Manage > Disk Management. If the disk is listed or hidden, right-click its graphic and change the drive letter to one nearer the end of the alphabet.
5. Control Panel > Add New Hardware and let the wizard find it.
6. Look here, particularly numbers 3 and 4 here http://support.microsoft.com/kb/871233/
7. If you have one, or can get hold of one, try using a ‘Live’ Linux CD to determine whether the problems are hardware or operating system related, i.e. if your USB ports work in Linux, then it isn't a hardware problem.
8. I‘ve been told that certain files should be in C:\Windows\Inf. I have 8 names each with an extension of .INF and .PNF, i.e. 16 files altogether: irstusb, usb, usbport, usbprint, usbstor, usbvideo, wceusbsh and wdma_usb.
9. Also, these driver files are present in Windows\System32\drivers\ . They have an extension of SYS and there are 13 of them: usb8023, usbcamd, usbcamd2, usbccgp, usbd, usbehci, usbhub, usbintel, usbport, usbprint, usbscan usbstor and usbuhci.
10. Have a look at USB troubleshooting tips here http://www.uwe-sieber.de/usbstick_e.html
11. Check the BIOS for these three settings:
Look for ‘USB 2.0 Voltage’, low, med, high or max‘. If it’s present, set it to max.
Check that USB legacy support is Enabled.
Under Plug and Play or Peripherals, there may be an option to clear the stored data of PCI/USB devices.