Windows 7 will not allocate drive for usb disk

you should try and assign your external hard drives a drive letter. do the following:

start-> run->diskmgmt.msc
hit enter
Right-click a partition, logical drive, or volume, and then click Change Drive Letter and Paths.

Do one of the following:
To assign a drive letter, click Add, click the drive letter you want to use, and then click OK.
To modify a drive letter, click it, click Change, click the drive letter you want to use, and then click OK.
To remove a drive letter, click it, and then click Remove.

for more info
http://technet.microsoft.com/en-us/library/cc757491%28W...