Help me please...

W7
First, please disconnect all USB devices and then perform the following steps:
Click "Start" button, type "devmgmt.msc" (without quotation marks) in the "Search" bar and press "Enter". Click "Continue" if necessary.
In Device Manager, double click to expand "Universal Serial Bus controllers", right click on the Host Controller, click "Uninstall" and click "OK".
Repeat the step 2 to uninstall all items under "Universal Serial Bus controllers".

Then, restart your computer and Windows 7 will reinstall all USB controllers automatically.
for xp or earlier
Click start right click on computer select properties device manager scroll down universal serial bus controllers you could see a yellow question / exclamation mark? ! or a red X
you will need to update/reinstall drivers
right click to reinstall drivers
if you can see your usb drive but its not working
ports (com&lpt) right click update driver if this fails to fix the problem
check the USB leads that attach to the motherboard usually red white green black make sure they are securely seated and have no dust build up on them dust will cause static and a lot of unforeseen problems to a computer and its parts
Click start click to open on my computer you should see your usb drive could be E: or something right click select properties there will be an array of options
select the sharing tab option then advanced sharing make sure you have a tick in the share this folder box
then click permissions make sure you have all 3 boxes ticked full control changes and read in windows 7
Click start control panel administrative tools computer management disk management right click on your drive select properties click tools you should see click check now click start two boxes
automatically fix files and scan for and attempt recovery of bad sectors place then a tick in both boxes then select check now start
you might tick one box then return after its finished the first repair then return and tick the second box you should not do anything while the chkdsk utility is in progress any input may damage this drive
then you restore it to its default status
Right click on usb drive select properties you will have an array of options
Select the hardware option then select your drive properties policies
restore defaults
In XP
Right click on your drive select properties then on customize restore Default in W 7
You might have to alternate doing this repeatedly until the problem is resolved
Click start control panel scroll to folder options view place a tick in show hidden files folders and drives
this may vary depending on your operating system.
https://tails.boum.org/doc/first_steps/usb_reset/windows/index.en.html