I can't see an external drive in explorer.

I have 3 external USB drives and 1 USB DVD drive as well as 3 HDD ATA drives with mucho disk space. Recently bought an 80 GB pata drive and installed it in an external case and connected to USB.
In my Explorer-Files (EF) I see all my drives but the new one. The new one is formatted and partitioned ok. Using the Device Manager & Computer Management-Disk Management I see the new drive as disk 3 and assigned the letter K but it still doesn't show up in EF.
I also use Power Desk Pro 7 and it doesn't see that drive either.
I connected the drive and cable to my Laptop with Win 7 and the drive is seen there in EF and PDP 7.
My pc is a Dell Inspiron 4600 with 3 GB Ram, 2.8 Ghz P4 running XP Pro SP 3. The pc has 4 USB connectors in the back and 2 USB connectors in the front. I also have a powered USB strip with 8 connectors. All are USB 2.0 connectors.
Thanks