I have Windows 7 in my primary partition and I installed Ubuntu 13.04 in the second partition. I deleted the Ubuntu partition and kept windows 7. Now the next day when I try to start my windows 7 I get an error:
I believe that the problem is due to the fact that you installed the grub bootloader on the MBR (Master Boot Record), overwriting the Windows bootloader. This is the default configuration when installing Ubuntu (and most other distro) since this is what you need when you install Ubuntu only (but also works with a Windows partition on the side). I generally don't like this and recommend not to do it. Instead, the grub bootloader should be installed on the Linux partition itself and the Windows bootloader should be kept in the MBR (adding an entry to chain-boot to grub on the Linux partition). This is what you did wrong, and the reason why it is broken now is because even though grub was on the MBR, its configurations were on the Linux partition that you deleted. So, now, you have grub starting but finding no configuration and thus the error message.
To fix the problem, there are a number of possible solutions. On this site, they have some simple instructions for recovering the Windows 7 bootloader, which requires having a Windows 7 recovery disk (or live USB). I think that if you have a Linux LiveCD (or USB) (like the one you used to install Ubuntu in the first place), you should be able to find the "Windows" option in the grub menu when you boot from that LiveCD/USB, and once you are in Windows, you can restore the bootloader with whatever program you choose, such as EasyBCD or BCDedit.
The next time you want to install a dual boot setup, be more careful about how you configure the bootloader and where you install it. As I said, I prefer having the Windows bootloader on the MBR, add an entry to it using EasyBCD for loading grub, which you install on the Linux partition. This is much more robust (if either OS gets corrupted or fails or is wiped out, you will not lose access to the other).
There is also a Win7 and XP tool that can restore the Windows MBR. The actual problems is that the Grub boot loader is looking for the grub configuration files in the Linux partition, which don't exist any more. So, if you boot directly to the Windows recovery partition, or from a Windows recovery disc, you can restore the MBR and Win7 will go back to booting properly.