WD external hard drive not showing up on my computer

I have a desktop computer running on WIndows XP. I have a 1 TB My Book Essential external hard drive and I used it a while back to store a lot of pictures and now a a year or so latter and the same computer will not recognize it so I can access the info that is on it. Any suggestions to help??? Thank you.

check the connections… try with a different cable and a different computer… Also make sure to connect the drive directly to the wall outlet

Mine Book started to disappear yesterday  as well. Today it said you have to unlock it first before you can back up your files. Why now I never had to enter a password to back up. I unplugged the USB and plugged it back in The open file screen shows up. I can see the data on the drive and I copied some files before it disappear again… It does the same on 2 other computers. So I have no clue as to what happened. Still trying, the password screen never came up again.