Ubuntu not booting after dual installing with Windows XP SP2

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http://askubuntu.com – I have 2 hard disk in my PC (First one was divided into 3 logical drives C:\, D:\ and E:\ and the secondary Hard disk was divided into 2 logical drives G:\ and H:\ ) The former one was running Windows XP installed in C drive with the FAT32 file system for the former and the latter was in NTFS. I had some files in G:\ drive which i moved to H:\ drive before installing Ubuntu Desktop 12.04 LTS through Boot CD. The installation was done with part of G:\ drive (with more than 300 GB) was used as root (/) file system with about 10 Gig and Swap space of 6 Gig. After the installation, Ubuntu asked (HowTos)