Follow the steps mentioned below to remove the linux/ubuntu os in the pc which runs windows 7 without formatting the whole harddisk.
[The drive in which ubuntu is installed is invisible in windows 7] .
CAUTION:First change boot config,otherwise it can result in system boot failure.
CHANGING BOOT CONFIGURATION
1.Download and install easy BCD (free non commercial version)for windows7.click here to download.
2.Open easy BCD.
3.Click on BCD backup/repair
4.Perform all the actions Reset BCD configuration,Recreate/repair boot files and change boot drive to c[where c drive contains the files of windows7 os].
5.Now restart our computer.
1.Open control panel
2.Click on System and Security>Administrative Tools>Create and format harddisk partitions.
3.Now in the opened disk management window,you can see the Linux os drive there.Right click on that drive,delete it.
4.Use the unallocated space to create a new drive in windows.
Now you have successfully removed the ubuntu os.