Sumit and other Volunteers who helped me through this,
This method worked after about 100 hours of trying out so many methods. But there are some catches though.
I did not intend to a clean install but Windows showed some message to the effect that the Windows installation location is not proper and hence will only do a clean install. Having fought this problem for so long and also because I had backed up my data I clicked ok.
The installation went ok and I am left with a clean install of Windows now that is quite snappy though the Disk shows 100% in Task Manager.!
I did find my old files in Windows.old folder. It requires an Administrator access, which I gave but it does not open at all. I would prefer to copy the 100 GB something files from the existing hard disk rather than external hard disk. Is there a trick to do this?
Despite these two nuisances, I am happy overall. Thank you all again.