Unable to detect External Driver

Following are the input
- Use external WD HDD 500GB to save my data
- Brought the HDD around 9months back
- Working Laptop Window XP
- Whenever I plug my WD HDD to my laptop it able to detect and all my files are save in there.
- about 1 month back, suddenly unable to detect the external HDD driver.
- try to run the NTFS Recovery that time the files all able to detect but need to buy the recovery file to recover.
- Didnt recoer that time cause I dont have any extra HDD to recover.
- Today try to recover using the same method but unable to recover.

ANY ADVICE?
All my file in the External HDD are impoartant files.

PLEASE Advice