If I understand you correctly, you purchased the enclosure then removed the Seagate st36811a HDD from an Older Dell desktop machine. The Seagate HDD worked in the Dell desktop. Since you installed the drive in the enclosure have you tried to test the unit in a desktop machine running XP to see if it operates properly?
If it operates properly in a desktop machine with XP, transfer the files and folders to that machine, then use a USB flash drive to transfer your files and folders back to your laptop.
If the enclosure does not operate properly in the enclosure on a desktop machine running XP, then follow the instructions in post #16 with a desktop machine and see if the drive is recognized and if you can recover the data.
From information I can find on the drive, it is an old drive (vintage 1999) and the drive may have encountered some problems since it was removed from the original Dell desktop.