We lost some of ds's baby pics this way on a laptop we had 4 years ago. It was my fault, I did a system restore . We now do exactly what jmg suggested and all pics which are on the pc are also on two cds, one of which we keep and the other of which my parents have in case the house ever burns down . We have also borrowed family albums from the grandparents too to fill in any gaps that were left by my mistake .
I really hope you can get yours back though, as janh says they may still be there.