Memory I have an older computer and some time back I had to have a new motherboard and several other Items installed in it. I decided I wanted to upgrade the memory. I found a site and run the scan to tell what kind of memory I would need. So I found out it would take 3-256 MB PC100 DImm 168 Pin. which would be a total of 768. My problem is when we installed them it only recognizes 2 of the memory cards, which is 512 total memory. We Have installed them One at a time to see which one it is not recognizing and the third slot seems to be the one. Is there something else I can do to see why this is happening? the Mother board is a Shuttle AI61. Thanks

Ok well there could be a few things going on here. It is possible that A: your third stick is damaged which I'm assuming you dismissed through your installation of one at a time, B: the third dimm slot is damaged and is unusable, C: the dimm slot is turned off in your bios. 

Now looking at the Shuttle A161 motherboard it would appear you have a primary dimm slot and then expansion dimm slots (technically these are called the controller dimm slot and the estensions) 

The controller slot which is offeset from the other two should have your largest ram, make sure the ram you stick in this slot isn't a stick that requires dual recognition. Some ram is designed to work in a pair even in the early PC100 class ram. Most PC100 ram you'll find now requires the sticks to work in pairs and the ram is coded for this. (Especially since PC100 is on its way out very fast.) The expansion slots can be fitted with a pair that will work together. I doubt that your third and primary slot is turned off as it is the controller slot. If none of your ram works in this slot replace the old ram in to this slot and just use the two expansion slots. It may not be as much ram as you want but the motherboard has presets that are just problematic. 

My general advice however is, that if you're running this motherboard which is fairly out of date, I'd upgrade to a new computer. Buying a cheap Dell desktop or even a barebones off of newegg.com and transfering your current Harddrive and what not over would probably be easier for you and will carry you for the next five years or so.