WD5000N1G starts up but stops again before getting detected

I have a WD external hard disk. I was having a problem with it sometimes, so im lucky that i backed up all the data before it compleately stoped working. 

The problem is , when i connect it to my pc it starts up, and i can hear some flips( so that means harddisk is actually getting started), after a while (in 5 sec) it restarts. that happens again and again. So im not able to use it anymore.

I researched on the web, that probleam happens alot with WD external hd and that means it is dead. 

So once more i wantted to try my chance here. Anyone has any idea ?

(btw: i have vista - windows 7 and xp ( all are different ps ) so i tried it in different platforms and also in different pcs.

thanks for help