This is due to an issue in the BIOS where booting gets stuck due to ACPI and battery support. Refer this link https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1093217/comments/63.
Now start up a terminal window and type the following commands:
$ sudo apt-get install iasl <enter>
$ sudo cp /sys/firmware/acpi/tables/DSDT /home/user/DSDT.bac
$ sudo chown user.group DSDT.bac <enter>
$ cp DSDT.bac DSDT <enter>
$ iasl -d DSDT <enter>
Edit the DSDT.dsl file as shown at this link https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1093217/comments/63. You just need to add a sleep (50) at the specified line in the file.
$ iasl DSDT.dsl <enter>
$ sudo cp DSDT.aml /boot/. <enter>
Reboot and at the grub menu, press ‘e‘ to edit the linux line. Just before the ro, add acpi=/boot/DSDT.aml and press F10.
If this works, you may want to make the above change permanent, you need to edit /boot/grub/grub.cfg and the the words acpi=/boot/DSDT.aml to the line that starts with
linux /boot/vmlinuz-3.5.0-23-generic acpi=/boot/DSDT.aml …. and so on, in the file.
Remember that each time you upgrade the kernel, you need to edit the /boot/grub/grub.cfg file to re-instate acpi=/boot/DSDT.aml.