Follow these instructions to get to a command prompt (and backup your files if needed). You should be able to use your system recovery options for this (no need for a DVD then).
Follow the tutorial to take note of the letters of your drives (C:\, D:\ etc.) from Notepad's "Open File" dialog. They may be different in an environment like this: for instance your recovery partition may be labeled "C:", and your Windows 7 may be labeled "D:", although this is rather unusual. Take note of their sizes too.
Then mark your Windows 7 partition as active. Use the following commands:
(you are now inside DISKPART>)
select disk 0 (select the hard drive with Windows 7, sizes in bytes are shown)
select partition 1 (select the partition with your Windows 7 installation, sizes in bytes are shown)
You can now try to restart. If it is not fixed, try to repair your bootloader. Change directory to E:\boot, where E: is your Windows 7 install DVD (check the drive letter):
cd /d E:\
Run the following command, where C: is your System partition (check the drive letter):
bootsect.exe /nt60 C:
Then restart your computer.