Fujitsu C352 lifebook lost bios need help

I recently upgraded my boyfriends laptop with a bigger hd and then found out he was planning to sell it so i put back the original HD but it keeps saying no Operating System found! i tryed my win XP home cd but just get the same answer. I also tryed the Ultimate Boot Disk and it still said no operating system found!! Tryed to chat with 2 different techs at fujitsu website and both of them seemed to lose connection instead of answer my question they seemed to just fade away…lol No one has an answer. I have even tryed to put back the larger HD but it keeps saying the same. BTW both HD’s previously worked just fine on this lifebook!
PLEASE HELP ME……ty