I built BartPE on a USB drive but it couldn't see the hard drives. Turned out I needed drivers for the SATA drives on my new PC. These were the steps:

1. Extract/install the DriverPacks Base program to C:\DPsBase\
   
2. Download the latest Mass Storage DriverPack directly to the DriverPacks folder: C:\DPsBase\DriverPacks\
   
3. Run C:\DPsBase\DPs_BASE.exe
   

Detailed instructions: http://driverpacks.net/docs/Miscellaneous%20guides/driverpacks-base-bartpe-guide