no HDD detected

possible motherboard problem
I have a home built computer. Built 2 years ago. Worked great for a long time and began screwing up several months ago.

System info:
AMD 1.2 ghz processor
Asus A7A266 motherboard with award bios
512 mb of DDR ram
(1) 40 gb Maxtor hard drive
(1) 80 gb Western Digital hard drive
XP Operating system

Now for the problem i have experienced in the past.
My secondary hard drive could not be detected. the 80 gb hard drive. I did not have time to work on this problem and was not that concerned about it at that time. Very little data was stored on this HDD. Besides my operating system is on the 40 gb HDD. so my computer was still functioning.

Now for the problem at hand.
Well it appears that my 80 gb HDD is now being detected but, the 40gb HDD has gone away now. Rendering the computer useless. No operating system on the 80 gb HDD.

Now for what I have tried, I have replaced the ribbon cable with one from a working computer. No Luck here.
I have changed the pin settings to cable select on both HDD. Still only detecting the 80 gb HDD.
I have swapped the power supply from the HDD that the system was detecting with the one that it was not detecting. Still only seeing the 80gb HDD.
I have removed the 80 gb HDD and tried the 40 gb HDD alone. NO LUCK HERE EITHER.
replaced the hard drive with one from another computer that had an operating system on it. Still no luck.
SO I put the 80gb HDD back in and installed an operating system on it. worked for about a week and now it will not detect it.

I am not sure where the problem lies exactly but i suspect that my mother board has issues. Unsure if replacement is the answer or if there are other options. I can still access the BIOS without a problem.

Thanks for your help in advance.

What type of drives are these (ATA 100?)?
Are they both of the same speed?
Are they both connected via the same IDE cable?
Are you using the correct cable for the speed of drive you are using?

Unsure what type of drives are these (ATA 100?)? not sure what you mean. I can not find the paperwork on the equipment.

But i do know that one hdd is a 7200 rpm and the other issomewhere in the 5400 to 5600 rpm range.

They are both connected on the same cable as my motherboard only has one place to land this cable. I don't know of any other way.

As for the correct cable for the speed of the HDD, I was unaware that they made different types.

Well I learned something today. It turns out the video card was not pushed into the AGP slot completely. As for the 40 GB HDD it is toasted. Fried. Trash. One ugly paper weight.
Have a good day.