The error bootmgr is missing is expected for a blank drive which is what you have after using DBAN.
More than likely you need to load the Intel SATA drivers during installation otherwise it hangs up like you have experienced.
See Windows Reinstallation Guide/A Clean Install of Windows 7:
http://philipyip.wordpress.com/dell-community-forums/
The SATA drivers for this model are listed under chipset opposed to SATA http://ftp.dell.com/chipset/R228085.exe to prepare the preinstalaltion SATA drivers see Step 6 and extract this .exe with 7zip, copy the f6flpy32 or f6flpy64 to a USB stick depending on whether your system is 32 bit or 64 bit respectively.
Load them during the Windows installation (Step 8) before you select which hard drive partition to install Windows 7 on. With any luck the installation should no longer freeze up.
Once Windows 7 is installed install the rest of the drivers (you will need to install R228085.exe also to get the application).
