Digital BW, The Print

I have a Scanmaker 4 with trays for 4X5 and 35mm negatives.  When 
trying to scan images with detail in shadow areas, the resulting 
image shows none of this information.  Instead, I get straight 
black.  Curve adjustment in the Twain package doesn't seem to bring 
very much of that detail out.

I'm still a little new to using this scanner with my negatives.  Is 
there something I can do to capture all of this information for 
manipulation in PhotoShop?  Is the detail really there already and I 
just don't know it (or how to access it)?  I would like to get into 
printing digitally, but need to get over this immediate hurdle first.

Thanks.