In Vostro 1520 Dell Laptop series, when Ubuntu installed with windows (Dual Boot), due to a problem in bios the MBR will get corrupted and after that you will be unable to see the Grub loader at the startup and you want be able to load either windows or Ubuntu. This happens only because of the corruption at MBR record or partition table. So by reinstalling grub to the partition u can resolve this problem. The steps of resolving are given below. First you have to boot from the Ubuntu Live CD Then you have to find the sd number of the partition that grub is installed in. ( If you have a separate /boot partition it should be the boot partition sd number otherwise it should be the Ubuntu file system sd number. ). And here I assume that sd number is x . Open the Terminal and execute following codes sudo mkdir /mnt/root -- Setup a folder before change root. Using this code Mount the partition in to the folder created. sudo mount -t ext3 /dev/sda x /mnt/root Mount and