1TB hard drive doesn't work

I have 1tb wd elements external drive for 2 years. I plugged it my computer yesterday, I saw my files but suddenly hdd windows blocked then it’s icon has lost in my computer . I plugged again but it didn’t work. I have seen it’s blue led is working. 
I downloaded data diagnostic software but I can not test my HDD. I have seen only “WD” caption, there arent any more informations. so test wasn’t be successful. What can I do if my hdd completely fail?

WD Elements model WDBUZG0010BBK buyed this month is not acepted on PC with Windows Vista 7 Premium while it’s working well on other PC. can it depend of an Office 2003 instead of an up to dated program?

Led of WD Elements lights continuously just after plugged but after ten minutes it repeat on-off.

What you suggest i ahve to check?