I successfully launched an instance. However, I could not ping or ssh into that running instance. By viewing the instance's console log, I found out that

Booting from hard disk
Boot failed. not a bootable disk
Booting from ROM
DHCP (net0: fa:16:3e:3e: 23:aa:bd)
No more network drivers
Booting from floppy
Boot failed. Could not read from the boot disk.
No boot table device

Openstack dashboard shows that the instance is running without any errors (status is Active). What is wrong about the image? why it is running but its log is saying it is not bootable?

Nova logs show:

# cat /var/log/nova/compute.log
2013-05-09 10:58:23.063 WARNING nova.virt.disk.api [req-fb03d308-6390-4b0a-bb68-02a1fe896a7b e8ed005baf2d4999a7680899e0a27450 654ae45fb88241de9a80e228fa47edf8] Ignoring error injecting data into image (No operating system found in /var/lib/nova/instances/fe3c1bd4-4e48-4ae6-8efd-ae03b103028b/disk)