Added 1Gb RAM DDR2 533 PC2 4300 CL5 but recognizes only 512Mb

Where they purchased as a working pair some motherboards will only accept working pairs>?
Make sure RAM modules are of same brand and type try one ram module at a time in the working slot closest the cpu if both work individually they are not a working pair

It may be compatible, but is it also rated as compatible by the Dell website? and is it the same type of RAM as your old RAM? According to the Dell website your system comes with 2GB as standard and will only accept 4GB maximum. The fact that the system doesn't start with only the new RAM and is fine on just the old RAM would indicate that your new RAM is not compatible or is faulty.

If you added another 512Mb RAM to increase the RAM to 1Gb then the new 512Mb memory stick could be incompatible with the original 512Mb or it could be faulty.
Use RAM that is same make and speed as the original RAM.
Remove both RAM and just insert the new 512Mb into your laptop and see if the laptop boots up, if not then the RAM could be faulty.

Hi - according to memory suppliers your T23 has the following memory capacity / requirements:

• IBM ThinkPad T23 maximum RAM capacity: 1GB
• Your IBM has Two (2) memory slots or sockets
• Module upgrade PIN count is: 144-PIN
• The memory speed is: SDRAM 133MHz, PC133
• The laptop DIMM type for the ThinkPad T23 is: SODIMM, SO-DIMM, Small Outline DIMM
• Non ECC

If you are meeting these requirements, you may have a defective module.

Also, according to Lenovo's page on the machine:

Memory
The system has 128MB or 256MB of memory standard and can be configured for up to 1GB of addressable memory. Memory options up to 512MB SDRAM SO DIMMs each can be added in the two available slots for memory expansion. The standard 128MB of memory is expandable up to 640MB and the 256MB of memory is expandable up to 768 MB of addressable memory with 64, 128, 256, or 512MB SO DIMMs without removing the 128MB SO DIMM that is standard in one of the internal slots for memory. For customers that need the maximum 1GB to which memory can be expanded, it is necessary to replace the 128MB or 256MB card with a 512MB card plus add another 512MB card in the extra slot. Only 133MHz DIMM memory can be used in this system. The use of 100MHz DIMM memory is not supported in the T23 systems.

This means yo can trouble shoot the 512MB modules individually by installing one of the original 128MB modules and one of the new 512MB modules (for a total system memory of 640MB). If it does not boot, try again with the other 512MB module. This will help you identify a defective module that may be preventing the machine from booting.

I hope this helps & good luck!

Remove both sticks of RAM. Insert the "new" RAM where the "old" RAM was, and see if your computer reports "zero" RAM or 1GB of RAM. If the latter, put the "old" RAM into the "second" slot, and see if the detected RAM is the sum of the two sticks.

is the computer able to take that much ram? or does it max out at 1 gig?

There is no reset just because you added memory.

If you have 2- 1GB sticks, try both , one at a time.

Your system spec's and manual tell nothing which dimm banks are suppose to be used , and if you can install 2-1GB sticks,
all it says is it can handle 2GB.

Now it says 512MB, sticks, this could mean you can only use 4-512MB sticks to get too 2GB,.

Now it does not tell which dimms are used if you have 2-1GB sticks,

You have 4 slots, the first two and the second two, most times, you either use the second bank of each pair, or the first slot of each pair,
but as I said, your system does not say.

So you can try both ways and see if one of them work.

Sorry I can't be of more help,but you system has a poor manual
on memory placement.

Once you change the ram, you have to boot to the system setup so that the BIOS can recognize the new module.
When inserting the ram module in the slot, it should be at a 30 degree angle to the system and inserted till the golden contacts can not be seen looking straight down at the slot. Then press the module down until the retention clips click. The top edge of the contacts should then be barely visible.
Once the RAM has been properly inserted, then boot to the system setup, exit then boot to windows

there are basically three different kind of ram so dear if its not working go out there and get the compartible one for your computer pls dont destroy that baby of yours.

I assume the laptop had originally 256Mb RAM and you put 512Mb RAM in a the spare memory slot and you expected to see 768Mb of memory, is this correct? Try removing the 256Mb memory module and insert the 512Mb memory module and see if the laptop boots up with 512Mb of RAM. If it doesn't boot up then the RAM is either incompatible or faulty. Try using RAM modules from the same manufacturer.