it's bu@@ered
you have two heads and plenty firmware that actually covers a frightening number of different file systems and formats (4 variable power heads if rw)
if one head goes ... you often get one working and not the other .... or read but not write etc etc
you can get a new one (for desktop) very cheaply
for a lappy ... best to get a usb one
however
first check the conections .... remove the drive from system | hardware manager
redetect ... and see if reloading the drivers works
failing that ... on a desktop you need to know if it's IDE
http://images.google.co.uk/images?hl=en&rlz=1T 4GPTB_en-GBGB295GB295&um=1&sa=1&q=ide+connecto r
or
sata
http://images.google.co.uk/images?sourceid=nav client&hl=en-GB&rlz=1T4GPTB_en-GBGB295GB295&q= sata+connector&um=1&ie=UTF-8&ei=4DjWScCwOpXWlQ f0pYzODA&sa=X&oi=image_result_group&resnum=4&c t=title
to make sure the new one will fit