Memory Issue

[Airesz]

Ok I have what may prove to be a simple question. About one year ago I bought an HP Pavilion 505w running Windows Xp home edition. My computer came with 256mb of memory I added a 512mb chip a few days later and that I thought I would have a total of 768mb but my computer is only reading a total of 512mb of memory and up till a few days ago I thought that my motherboard was only able to support 512 of memory. I visited http://www.crucial.com/systemscanner/ and ran there system scan and they told me that my computer was able to support 1024mb of memory I have been unable to find out why my computer is not showing both modules.

In the first slot I have a Kingston 184-pin DIMM DDR PC2100 512mb module
In the second slot I have a Kingston 184-pin DIMM DDR PC2100 256mb module

I have tried to reverse them to see if that would have any effect and it didn’t

My System Information
Computer Manufacturer HP
Computer Model Pavilion 505w
CPU Manufacturer GenuineIntel
CPU Family ntel(R) Celeron(R) CPU 2.20GHz
CPU Speed 2191 MHz
Front-Side Bus Speed 100 MHz
Currently Installed Memory 512MB
Maximum Memory Capacity 1024MB
Total Number Of Memory Slots2 (2 banks of 1)

Other System Info

Main Circuit Board
Board: ASUSTeK Computer INC. P4G533LA REV 1.xx
Bus Clock: 100 megahertz
BIOS: Award Software, Inc. 3.05 12/18/2002

2.20 gigahertz Intel Celeron
8 kilobyte primary memory cache
128 kilobyte secondary memory cache

I hope I have given enough information for you all to assist me with my questions. Thanks in advance.

Could some tell me why my computer only sees one of the memory modules?

[ski]

Is only 512 MB recognized in both BIOS and in Windows with both modules inserted?

If so, then make sure both RAM modules are fully inserted.

If ok, then clean off their contacts with high purity(91% or higher) alcohol.

If no luck, then insert just the 256 MB module.
If it's not recognized, then it may be bad.

If it's recognized, then run Memtest86 to check it.
If it passes, then insert just the 512 MB module, and run Memtest.

If it passes, then insert both modules, and run Memtest.
If the system and Memtest recognize just 512 MB, then the 2 modules do not like being installed together.
If you want more than 512 MB, then you may have to install another 512 MB module.

If the full amount is recognized in BIOS, but only 512 MB is recognized by Windows, then check for a Windows configuration that limits the amount of RAM that it can recognize.