A few things to try.
1. Try different USB ports on the computers in question.
2. Be aware that some IT people might disable the USB on servers as a security precaution, can you successfully connect any <i>other</i> drives to these computers? Does the account your using have the USB ports disabled by the admin?
3. Try the add hardware control panel and see if it is found during a scan.
4. Download the latest USB drivers from both the computer supplier and the maker of the drive your attempting to connect.
<a href=”http://www.smartcomputing.com/editorial/article.asp?guid=&bJumpto=true&Isfrm=IN&article=articles/webonly/techsupport/457w10/457w10.asp&ArticleID=48875″>Here</a> is a good resource that deals with this problem.
Some of the USB ports may not support “<b>USB 2</b>”. This can cause the computer system to ignore the device. If this is the case, ensure that the motherboard supports USB 2, and purchase a USB 2 hub card. (I know – I had this problem and it took a few days to finally sink in.)
This is obviously a compatibility issue between your backup disk to your computer system. Make sure that the type of the USB port your are using for your external hard disk is compatible with your computer unit like USB 1.0, 2.0 or 3.0.