Anilrgowda

Question
My system will not boot. It gets as far as the Windows XP logo with the 'busy bar' going back and forth, hangs for a while, and then reiterates the entire reboot process. Starting in Safe Mode reveals a hang at MUP.DLL.

I booted Partition Magic from a bootable CD and discovered that the primary partition has no drive letter allocated to it. Running FDISK shows the same problem, but I can't seem to do anything about it. I tried PQBOOT, too. (There is also a small partition which is described as FREESPACE. It has no drive letter either)

How can I restore drive letter C without erasing the entire operating system?

Solution
. you might have been infected by a virus and this damaged some parts of your operating system or even changed the partition table, so you have the 'no C:\ letter' problem. In such case, I don't think you can just restore the C drive letter. You would probably have to reinstall the whole operating system.
You might also try to plug your hard drive to another computer that has a working OS (and some good antivirus on it) and see what happens. If that OS can recognize your drive, you can copy any files that you need from the Windows folder and perform new installation on your own computer.

2. the other option is that your hard drive is damaged. In such case, I'd also try to plug the hard drive to another computer (with working operating system and some antivirus installed) and check if that computer can see the drive. If so, I'd copy as much data from the drive as possible and buy a new drive. You might be able to mirror those parts of your damaged disk that work and restore them to a new drive, althought, I don't know any applications that can do it.