If the camera is fairly new then the version of ACR you have with CS5 won't be able to read those file. You'll need to upgrade to a newer version of Photoshop or use Lightroom 5.
Once a new version of Photoshop comes out Adobe does not support updating ACR from the older version of PS.
We'll need information as to the particular Camera model your raws are coming from and your version of Windows.
CS5 only supports ACR 6.7.