External Hard Drive is not reconized on several computers

Hello All,
I have a HP Pavillion which I usually just have the usual maintenence problems with. I have tried to plug in two USB External Hard Drives,
which the computer does not read.
I then tried them both on my Sony Vaio. Still when I click on My Computer
it does not show that the drives are attached?

Help? I keep most of my pictures on these hard drives and I hope I didnt
loose the info on them.

Many Thanks for your help!
Cathy

 

Oh, and My desktop is Windows XP and My Sony Vaio which is a laptop is Windows Vista.
Both external hard drives worked fine for several years.

 

Is the activity light Blinking ?? if so try all ports USB HD's can be finniky, I have a devil of a job to get my recognised having to plug/unplug several times then its a hit or a miss affair, take to other computers and alls OK. Have you tried booting up with it attached ???