It was quite hard to get the system to get into installation mode through the windows install CD or when trying to boot from one of the PE based boot CD’s (BartPE, Ultimate Boot CD) on Dell Optiplex 755. The main culprit was the SATA harddisk and DVD drive, since the drivers for these models are not available (even after making a BartPE from the already existing Windows Installation).
The best method to overcome the problem was change the Drive Operation settings in the BIOS to “legacy” mode, so that they show up as normal IDE drives. I guess I am feeling the drives have become bit slower now, but that’s the compromise needed to be taken in order for installing/reinstalling another version of Windows.