HELP - External WD Elements

Hi, My hard drive WD Elements (2TB) recently starts to work not stable. Without any reason, I had problems to move or copy some files from my HDD. Sometimes my computer doesn't recognize my HDD. I tried to use WD Data Lifeguard Diagnostic for Windows "Extended Test", but it failed because some errors. It doesn't even want to finish the test. It just hangs around ~15% of scanned sectors...