How many drives have you tried? Have you tried those in other computers? Sounds like
you might have a group of bad drives. It is also possible that the system is taxed and can't
support more USB devices (possibly indicating a weak system) and a 'Powered USB Hub' might
work. For a PC the on-board USB can be disabled and an add-in USB card can be used which
is not expensive.
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Make a Restore Point so you can get back to where you are though it should not be needed.
How to Create a System Restore Point in Windows 7
http://www.sevenforums.com/tutorials/697-system-restore-point-create.html
How to Do a System Restore in Windows 7
http://www.sevenforums.com/tutorials/700-system-restore.html
References to Vista also apply to Windows 7.
Do these to clear corruption and repair/replace damaged/missing system files.
Start - type in Search box - COMMAND find at top of list - RIGHT CLICK - RUN AS ADMIN
sfc /scannow
How to Repair Windows 7 System Files with System File Checker
http://www.sevenforums.com/tutorials/1538-sfc-scannow-command-system-file-checker.html
Then run checkdisk (chkdsk).
How to Run Disk Check in Windows 7
http://www.sevenforums.com/tutorials/433-disk-check.html
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Then lets refresh the USB Stack
Control Panel - Device Manager - click anywhere in the blank/white area - then VIEW -
Show Hidden Devices
Now look everywhere EXCEPT USB Controllers for your device and if you find them (may have
more than one of each) under Disk Drives you may have several - RIGHT CLICK and UNINSTALL
for all instances. (There may be none.) (The device here is one of the drives you can't find which
may or may not be present in this area.)
Control Panel - Device Manager - USB Serial Controllers - RIGHT CLICK on EVERYTHING and
UNINSTALL all except the category itself - REBOOT - this refreshes the drive and the USB stack
This KB shows the XP how to and the Vista and Windows 7 methods are identical
http://support.microsoft.com/kb/310575
Here is a utility to help but do the above 1st.
USBDeview is a small utility that lists all USB devices that currently connected to your computer,
as well as all USB devices that you previously used. Run it Options and check the 1st three choices
to see if any are there.
http://www.nirsoft.net/utils/usb_devices_view.html
You would remove all instances of the devices then reboot.
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If needed try both of these :
Tips for solving problems with USB devices - and a Mr Fixit
http://windowshelp.microsoft.com/Windows/en-US/Help/c39bd203-f729-47a4-8351-83291e13c8a81033.mspx#EGB
Hardware devices not detected or not working - Mr Fixit
http://support.microsoft.com/gp/hardware_device_problems
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This might be helpful to determine if incorrect driver is loading.
DriverView - Free - utility displays the list of all device drivers currently loaded on your system.
For each driver in the list, additional useful information is displayed: load address of the driver,
description, version, product name, company that created the driver, and more.
http://www.nirsoft.net/utils/driverview.html
Hope this helps.