I added an additional 1GB of RAM card , but my computer will not recognize the additional memory. I tried swapping cards between the two slots , nothing . The specs say the motherboard can handle 1GB per slot - 2GB total . That's what I have now. Is it something in the BIOS or another setting I don't know about ? HELP !

try resetting the computer, if that doesn't work it could be that your computer only recognizes 250mb or your BIOS needs to be configured.

Is the memory the same size ?and belive it or not some machines don't reconize ram even thought it is installed ,if it is running good and your os reads the ram 
don't worry about it if not let me know 

try each ram one by one. if there is prob in ram it will show only 512 instead of 1 GB.. Second check for memory shared in bios

How much memory did it have before you removed the 256Mb RAM?
If it had 756Mb RAM then the memory in the laptop has 512 Mb plus 256 Mb RAM modules, the 256Mb in the slot you can see and possibly 512Mb in a slot under the keyboard or soldered on the motherboard.
Therefore by removing the 256Mb and replacing with 1Gb memory module will give you a total of 1.5Gb

Ram should always be paired. Same type, speed and size in each slot. You may have 1 SIMM/DIMM/DDR that has 2 sides of chips and the other with 1 which will do exactly what you state. RAM reads across the chips simultaneously. So if you have a different one in each slot it can go bonkers and do goofy stuff on you.

you buy the memory here for a great price or anywhere online instructions are on the page
it replaces the 512
http://cgi.ebay.com/1GB-DDR-333-for-Toshiba-Satellite-A75-S211-Memory-RAM_W0QQitemZ250353026446QQihZ015QQcategoryZ158897QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Memory Card for Toshiba Satellite A75-S211 Memory RAM- Designed and Optimized

Toshiba Satellite A75-S211 Memory RAM Memory Upgrade -Easily installed

More Memory Equals - More Speed for your APPS

The Toshiba Satellite A75-S211 Memory RAM has a memory card slot or slots, that allows you to add more memory to your Toshiba Satellite A75-S211 Memory RAM, giving you enhanced performance and speed. You will see the Immediate speed increase in your computers performance.
Stop waiting for programs, and functions to happen, STOP WAITING!!! Start enjoying technology as you should.
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Worry Free Installation: Just Follow these Steps Desktop and Laptop instructions below.
Desktops

1. Unplug Power cable
2. Remove Case
3. Slide memory card in Open slots- the memory card will only fit in one way
4. Snap the side clips in place
5. Close Case and Power Up
6. You are ready to go.

Laptop

1. unplug and remove Battery from laptop
2. Open memory compartment on bottom using Philips screw driver
3. inset memory in open slot, if no open slot remove current memory by pinching metal clasp on side of memory
4. Close compartment and power up you are off and running.

Are the memory cards the same? Try swapping the memory cards inside the computer. It is also important to go into the Setup (F2) once the new memory has been added. The setup keeps track of the hardware changes to your computer, and the additional memory needs to be saved in the Setup configuration. Please let me know what happens and thank you. Binary Bob

Here is the problem, the laptop take 2GB RAM. 1GB in each slot, so get 2X1GB RAM. They are cheap now. You need 2, 1GB sticks of ram. For cheap prices go to Newegg.com

Have a nice day!

Have you tried switching the RAM cards? What happens?

have you tried looking for an updated bios version for your motherboard?