in general, bad sectors cannot be recovered. however, if the damage is not too bad, then this software called "HDD regenerator" claims to recover them.. running a chkdsk or scandisk complete scan(at the surface level) wud fix ur bad sectors... u can also try this software but i dont think its a freeware!! i havnt personally tried it. their homepage link is here
also try Hdd monitoring utuility frmm www.panterasoft.com
u can get lott info onur HDD
yes do scandisk frequently
back ur important data as there may be little life span of ur HDD
also u can try out this link at ur own risk
*www.hackaday.com/entry/1234000840067578/