It sounds like Ubuntu took something or damaged something while being uninstalled. You might need to restore the Windows bootloader. To run the Bootrec.exe tool, you must start Windows Recovery. To do this, follow these steps:
- Put the Windows 7 installation disc in the disc drive, and then start the computer.
- Press a key when you are prompted.
- Select a language, a time, a currency, a keyboard or an input method, and then click Next.
- Click Repair your computer.
- Click the operating system that you want to repair, and then click Next.
- In the System Recovery Options dialog box, click Command Prompt.
- Type Bootrec.exe, and then press ENTER.
See more here.