I think I should have posted this 5 hours ago when it all began and which now follows in the below lines.
So I had Ubuntu installed on my friends laptop and she wanted to remove Ubuntu and install windows. So I made a flash bootable USB drive with Windows installer in it, and tried to install however installer won't detect Linux partitions.
Did a bit of reading here and there, and found that RMPrepUSB + Grub4USB + Partition wizard in single USB drive can help format Linux partitions, and so I did, and again windows installer won't find the partitions...
Then with some more googling found the FIXMBR command and tried that too, still no go.
Finally I came across a very powerful utility (makers make it explicit to accept that they are not responsible for whatever you do with it) called ultimate boot cd, used it with RMPrepUSB + Grub4USB and slip streamed Windows in it. Tried to load window, it gave a bSOD. So I performed a DOD WIPE followed by a format in NTFS using partition magic also slip streamed using RMPREPUSB etc etc
Now when I try to install windows it says HDD is not recognizable or corrupt. What should I do now? It is not even showing the HDD as un-partitioned or partitioned space or anything...
Just shows USB drive that I am using to install as the only disk recognized.
Basically, if you can't see it from BIOS/UEFI, there's something wrong with the hard disk itself and she needs to get a replacement drive for the laptop.
If you can see it under BIOS/UEFI, I would suggest using something like a Linux LiveCD/LiveUSB to do a zero-fill to wipe the drive. When booted to the live media, if you aren't sure which device to use as the target of the zero-fill, use the fdisk -l command to find the device that matches the expected size of the harddisk (you can also use something like smartclt -a /path/to/suspected/disk to ensure that it's the disk you want to wipe.
Once the disk is wiped clean, the Windows installer should see it as a possible disk onto which it can install. Let us know what you find.