This part confuses me, Cherkassy.
"I have installed the XP operating system from a pair of 2003 XP setup discs"
As this is a new build (I assume?), you need to install XP from an XP CD, not "a pair of 2003 XP setup discs" or a manufacturer's restore disk. It wont boot until you do that. Get an XP CD, set the BIOS to boot from the Lite-on drive, insert the XP CD, restart the PC, Press any key to boot from the XP CD and follow the onscreen prompts to format the drive and install XP.