This article will tell you how to work around the Error Loading Operating System when starting up Windows XP.
The Error Loading Operating System may be expected when installed a Windows XP system and restarted. While the machine is starting up, the computer's BIOS and CMOS will check the system's hardware and the operating system. If something is wrong, the BIOS and CMOS won't launch the operating system. When this issue happened, you can't get into your Windows desktop. Other systems like Windows Vista or Windows 7 won't display this message. If your problem is that unable to load Windows Vista or Windows 7 without this message, just try Startup Repair with the Windows Installation Disc.
1. The BIOS on the motherboard does not support the hard drive's size or settings.
2. The hard drive is not properly setup in CMOS.
3. There is something wrong with the hard drive's partitions.
For cause 1 and 2, update your motherboard's BIOS if possible by referring to the computer's manual or visiting the manufacturer's website, and go to CMOS setup to make sure the hard drive is detected correctly and at the same time, change the "Access Mode" to Large or LBA to add support for large capacity of a hard drive.
Inappropriate hard drive settings and partitions will also cause errors in the loading operating system, including the Partition table (part of Master Boot Record - MBR) error, MBR error, and wrong active partition.
Note: sometimes, the particular disk manager is required to wipe your hard drive and make partitions to Fix the Error Loading Operating System issue. If there is one from the hard drive manufacturer, it's usually the best one to operate your hard drive like wiping, erasing, and write zeros to the hard drive. If no, you could try KillDisk (free version is enough.)
With the wrong operations to fix error loading operating system will result in hard drive partition and inaccessible data, and data lost from your hard drive. You do not have a recent data backup. Under these circumstances, you will need a powerful hard drive data recovery tool to retrieve your data back.