In my laptop earlier I had Windows 7 32-bit installed and then I had formatted the complete hard disk to ext 3 and installed Linux Ubuntu. Now I want to install Windows 7, but when I try to install windows 7 the boot-able Windows 7 USB stick, the installer could not recognize my hard disk. How can I solve this problem and install Windows? Should I format the whole hard disk and convert it to NTFS using GParted?
Regardless of what filesystems you currently have on your hard disk the Windows installer should still see the hard disk (ext partitions be labeled unknown). If the installer isn't seeing any hard drive at all then it's probably down to missing IDE Controller drivers.
Look for RAID/F6/IDE Controller drivers on your laptop manufacturer's support page for that specific laptop.
Go to the above link and download the "f6flpy-x86.zip" drivers (second row) and extract those files on to a USB.