MBR boot record changes

I have installed on their computer window7 and ubuntu12.04 ( non- wubi), have been in use before window7 boot record to boot , but ubuntu in an update , you can not open : select ubuntu from the boot screen after the plane has been black , only in the upper left corner there is a cursor flashing. Later, I found a way to repair the grub boot :
1, install ubuntu with U-disk boot into Ubuntu system , ( ie, probation ubuntu)
2, open a terminal and enter the command
sudo-i
fdisk-l
3, see the information that appears terminal , remember your ubuntu system is installed in which partition ( if there is also a note of the root partition ) .
4, if your ubuntu / partition is sda7 and if the / boot partition is sda6, enter the terminal
mount / dev/sdb7 / mnt
mount / dev/sdb6 / mnt / boot
( if not / boot partition alone skip this step , this step is very important, no prior / boot partition installation have failed )
grub-install - root-directory = / mnt / / dev / sdb
exit
fix the end of the reboot , you can enter ubuntu , but this time into the selection of the interface is not window7 but by ubuntu boot screen. I am worried that after ubuntu unstable again after a problem can not open windows, how to modify the way to restore the beginning
------ Solution ---------------- ----------------------------
before you is how to use windows7 boot ubuntu 's ?
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To achieve the functionality you need to do the following steps:

1 deleted mbr of grub, this use diskgenius and windows7 installation CD can be done . ( deleted , you can not see the grub boot the interface )
2 essybcd in windows7 install such software to increase the grub boot entry to the boot partition boot from ubuntu .
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- ---- Solution -------------------------------------------- < br> If you try it, do first step 2 , step 2 in the confirmation do after a successful first step,
avoid linux can not start .

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Thank you for your answer, I have found a solution . I first used a tool called mbrFixer.exe repair a bit master boot record, the grub is deleted, leaving only NTLoader, then use EasyBCD add a BootLoader, was restored to what it was before .
------ For reference only -------------------------------------- -

Thank you for your answer, I have found a solution . I first used a tool called mbrFixer.exe repair a bit master boot record, the grub is deleted, leaving only NTLoader, then use EasyBCD add a BootLoader, was restored to what it was before .  
In fact, with the same way you start to say that I was I do not have the windows installation disk , then look for a long time to find mbrFixer this tool