already done that.
checked the box 'automatically fix system errors' first, it found some errors, then another run, it said the drive is healthy.
then checked the box 'scan for and attempt recovery of bad sectors' as well, it processed up to 72 files, it closed with no message.
crystaldiskinfo said 'caution'.. though it said caution to my pc's hard drive 'last year', still working..
now, i have installed wd data lifeguard diagnostics tool. smart status is OK. now, i'm running an extended test. though i'm afraid it will take ages..