Lost space on C drive

Yesterday I restored my Acer Extensa laptop, Vista Premium with 160gb hard drive and 2 gb mem to the factory default image using discs made when I purchased the laptop. On my C drive I now only have 28.2 gb when it should be 69.5gb and the D drive is 69.5gb. Have I done something wrong? Where has the space gone. There appears to be 50gb plus listed as unallocated!!! Can I regain the 50gb plus in anyway.