NTLDR is missing

Problem: Computer with Windows XP Professional operation system froze unexpectedly. No recent hardware changes performed, no applications recently installed. I reeboted. “NTLDR is missing” error occured.

I noticed that the system did not detect the hard disk drive where the operating system resided but I fixed this by reseating the IDE cables. Though the error persisted.

I then inserted the Windows XP boot CD in the CD-ROM drive in order to repair the operaton system. But I realized that if I changed in BIOS the Primary Boot Device from Hard Disk to CD-ROM, when the system asked if I wanted to boot from CD, I should not press any key and the system booted from Hard Disk. But this only happend if a bootable Windows XP CD was in the CD-ROM Drive.

While searching the Internet for solutions to this problem, i found this article.
No need for me to make a bootable anything as this guy describes here, but something caught my eye:

Once back into Windows, right click on the My Computer option, choose the Manage option. The Computer Management window will open, click on “Disk Management” on the left pane. One of the disks it lists, and one of the drives on it, will need to be marked as active. It will be which drive letter you have placed the 3 boot files into (this will likely be the C: drive on Disk 0). Right click on that drive letter and select “Mark Partition as Active”, you may first have to convert the partition to a Primary partition before you can mark it as active. Close and reboot.

I noticed that in Disk Management it was marked as active a partition on a slave hard disk. I wanted to unmark it, but I realized that I could not do that from the Disk Management interface.
Reading on the mentioned article, I found the solution to this last occured problem:
Mark Partition as Active with diskpart from Jim the Bean

I did that and it worked. It not only solved the active partition problem, but also my bigger problem as the system reebooted just fine with the Primary Boot Device set to Hard Disk and there was no need to set any partition as active on my system.