|A few bad sectors on a hdd is not a problem. I would consider 100 to be excessive.|
When they begin to breed this is a sign it is wearing out and should be binned soonest.
Consider if it failed suddenly such that it could no longer be accessed - this would be a nightmare.
One can re-format using an option to retest (rather than flag and bypass) failed sectors and reset as such if usable. However this is unwise, because they failed originally for a reason.
Replace *NOW*! After all, hdd's are not that expensive.
Good Luck - Keep us posted.