You may need to wipe the HDD first before proceeding with the Install. For this you can use either Boot & Nuke from DBam or Kill Disc.
http://www.dban.org/download
http://www.killdisk.com/downloadfree.htm
Boot & Nuke does a better job but with SATA Drives it may be easier for you to use Kill Disc.
However as already mentioned if Windows can not identify the hardware which with Dell's isn't uncommon you need to Slipstream a Install Disc with the Dell Drivers. Most notable the SATA or Chip Set Drivers and to do this you need nLite available free here
http://www.nliteos.com/download.html
Just don't forget to read the instructions available on the Web Site here
http://www.nliteos.com/guides.html
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