As you told, I disabled the Vista's CD/DVD handling feature by the mentioned registry hack!
After this change, I restarted my laptop so that the system might get refreshed completely. Even after the restart, when I inserted the helathy DVD (Data format, burnt by Nero 8), the windows was trying to browse for the data which was on the disc. The only change which I observed was, it was not ejecting the drive after browsing and found nothing (I mean, failed to detect the data on the disc!).
It was just showing the same message without ejection.
As I mentioned earlier, I tried for formatting. I inserted the bootable Windows Vista Ultimate DVD in the drive and restated the laptop. During the booting generally if any bootable disc is there in the drive, it shows an option that "Press any key to boot form the disc".
But here in my case it was trying... trying... for sometime and finally it is showing the following message on a black background.
Resetign the boot drive... _"
The cursor was blinking for some time at the last position.
By the noise and behavior of my laptop, I understood that it was browsing for the data, found nothing on the disc (Failed to find!) and finally loads the OS from the C:\ drive.
What does the message "Booting GRLDR..." mean?
Can anybody help me to fix this?