Well lets talk about the grub .People really face problem when they have dual boot windows and linux or some think like that .
suppose you have install windows after installing linux then you will see that your linux is not booting .This is because when you install windows after linux windows mbr replaces the grub of your linux.
Now for reinstalling your grub you can do this with the help of live cd of your linux distribution . but what if your cd drive is not working or you don’t have any external media to do that. so i am going to tell the most easiest way .
You can do it windows just download the software for window which is called a AUTO SUPER GRUB DISK . Just download it and install it and then double click it . After doing this just select the auto super disk and version 1 and then just click ok and it will tell you to reboot your computer . DO that and you will see the auto super grub disk option just select that and then select the recover grub option .After doing that you will be able to enter in your linux distribution .just reboot you pc again and you will see your grub again :D.
You can download it from http://www.supergrubdisk.org/.