1. What service pack level is the Windows XP CD you're using; original, SP1, SP2? Or were you using a System Recovery Partition?
2. What is the total capacity of the hard disk you're using.
3. What is the make and model number of the computer (or motherboard if not a "brand name" computer)? Older computers (BIOS) and operating systems did not provide native support for very large hard drives.
or
How old is the computer?
4. Follow Broni's advice.