Note: [u]Remove any other hard drives from your system you do not want dban to wipe. Proceed to wipe the operating system drive; this will take a significant amount of time, so be patient.[/u]
dban default is to wipe all connected physical drives in a system!

So you would disconnect any other separate physical drives beforehand if you wish to keep the data/files on them before beginning the dban operation.

It is safer this way than if you were to begin the operation and then specify which drive dban is to wipe anyway. Set the operation to write 0’s (zero’s) only to restore the drive to factory condition; any other wipe setting is overkill for your needs and will take much longer to complete.

Just the AVAST folder name alone indicates an issue with your Win 7 installation and not with avast! install per your screenshot, especially after finding out how you did the upgrade to 64-bit. Some 32-bit Win 7 files would be left behind and not overwritten when going to 64-bit and these files left over could impact proper operation of the 64-bit system.

OS drive C: should only have the operating system on it for best results; no secondary partition should be placed on it unless you create a dual-boot operating system drive utilizing Win 7 and (example) Ubuntu Linux, each on their own partition.

What is the make/model of your new hdd? Some issues reported with the hdd firmware being modified maliciously before being sold retail on several manufacturers not too long ago. Rare issue, not likely to affect you, tho.