you should try and assign your external hard drives a drive letter. do the following:
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 infohttp://technet.microsoft.com/en-us/library/cc757491%28WS.10%29.aspx