GA-7DX "error loading operating system"

My pc crashed last week telling me i was missing system files. I decided to wipe hd clean and reinstall. After cd loads files to hd, the pc reboots for the first time but comes back with “error loading operating system”
I have tested following components on different pc:
HD is ok - tested in other pc
Cabling is ok - tested on other pc
CPU is ok - tested with TuffTest
RAM is ok - tested with mem86, win diagnostics, & other pc
Power supply is ok - tested with other pc

Any suggestions? I’m stuck! Has anyone ever had this happen?

My PC:
Gigabyte GA-7DX BIOS is updated for REV. 4
CPU - AMD Athlon 1.33
Ram - 512
HD - single setup - WD 40G
WinXP Pro

check weather everything is plugged in correctly, maybe the IDE cable in the pc is damaged, i had a simaler problem to this about 2 days ago, and it turned out to be the IDE cable.

or maybe the Boot device priority has changed, and may need to be changed back again within the BIOS.

thanks for the response. I have tried 3 different ide cables so it’s not the cabling. In bios, i set it to boot cd-rom first, then HD, so that i could install XP. After the cd loads the required files to the hard drive, the pc reboots and asks to press any key to boot from cd. IF this is ignored, it is supposed to boot from HD. Unfortunately, it gives me the error message. I have tried changing the first priority to the HD just in case. Same thing happened.
I don’t think i will be able to figure this one out. I may have to trash the mobo.