You can restore the Windows bootloader with a Windows 8/8.1 DVD. These instructions are inspired by Manindra Mehra's answer, but I expanded it with full working details (verified with a Windows 8.1 DVD).
Put the DVD in your optical drive and boot from it. Press a key when it displays Press any key to start from CD or DVD. Select your language etc. and click Next. Click Repair your computer. Click Troubleshoot. Click Advanced Options. Click Command Prompt. In the command prompt window, type bootrec /fixmbr Click the red X to close the command prompt. Click Turn off your PC. Turn the PC back on and it should boot directly into Windows.