Well this issue is commonly observed on Dell lappys where I install Ubuntu by changing the default disk partition configuration. Windows fails to reach the login screen and exits after displaying a BSOD for a fraction of a second and reboots to show the options for booting Windows after it fails to boot. SOLUTION: The cure to this wierd behaviour is also weird. If you notice this happens only if your boot is not a cold start, as may be a reboot.

• What you can do is press the power button on your lappy for a few seconds so that it completely powers-off.
• Then press power button to 'cold' start it.
• Windows boots as normal.

Till the time I reach a permanent solution to this issue, this is what works for me; when I do, I'll puts it here. It surely has something to do with the disk partitions.