HDD gone wild

hello!

in my hands come strange hdd “ExcelStor J680” 80gb drive. strange because it’s losing patrition sometimes, sometimes in BiOS it’s shown only as $$$$$$$$ $$$$$ $$$$$$$$$ insted of it’s name & sometimes pc wont boot at all.
so i pluget it in to my pc to check it and nothing, no bad sectors, all parametrs normal [read, write, spintime andsomore]. then i unpluged it & start again but my own hdd “wdc wd1200jb-00dua3” also shown me “the dollar signs”! now it again works fine, but i’m woried about it’s health.
wher’s the problem, wath can i do. is it broken drive or something else?
Tnx.