Windows 7 cannot boot after Ubuntu install

Download Visual BCD Editor. It comes with "Dual-boot Repair". Install in XP.

If you have an installed Windows 7/Vista on any partition "Dual boot Repair" -> "Automatic Repair" will fix Windows 7/Vista booting.

Later when in Vista/7 you can add entry for booting XP (if missing) using Visual BCD Editor -> rightClick and select "Create missing Windows loaders".

Everything is done on click automatically - no parameters, partitions or what ever to specify.

It sounds like your Windows 7 disc is broke and you should try to create a new one.

Creating a bootable USB

If you have good internet connection, then you can download your windows 7 version here (you still need a legit key ofcourse).
Then you can use Microsoft own tool to make a bootable windows 7 USB.

• Start up Windows 7 USB/DVD download tool when you have downloaded and installed it
• Select the iso file you downloaded in the Source field and click Next
• Insert your USB drive which you want to use (4GB is enough)
• Select USB DEVICE and click Next
• Select the USB device you want to use and click BEGIN COPYING

When it is done, you should have a working bootable Windows 7 USB

The same steps are used for creating a DVD, just select DVD instead of USB device.

BCD Repair

Windows already have a tool for this purpose, called BCDboot.

If the system partition has been corrupted, you can use BCDboot to replace the system partition files with new copies of these files from the Windows partition.

When you have booted to the Windows disc, then go to the command prompt (see here) and type the following to recreate the BCD on the C drive:

1. attrib -r -s -h c:\boot\bcd - unhide BCD so it can be deleted
2. del c:\boot\bcd - delete the current BCD
3. bcdboot C:\windows - create a new BCD on the C drive

From here you should be able to boot into Windows again.