Weird Sony Viao notebook memory problem

[Kemist]

Hello all. I am a newbie here but this looks like a great place to post and lurk. I do have a hardware issue that I hope someone may be able to shed some light on. The problem I have is with my Sony Viao notebook PC. It is an PCG-NV170 which is basically a 1.6 ghz P4 machine. It has a tiny 16mbyte ATI video card on the board and came with 512 mybtes of system RAM. About a week ago I was using my computer on another discussion board and it froze on me while I was typing. I could not get it to boot again. After trying many things I found that if I removed one of the two 256mbyte memory cards the computer would boot and run. It does not matter which memory chip is installed as long as only one slot is populated. Either card will work but the machine will not boot when both memory chips are installed. Unfortunately the BIOS on my machine will not support a single 512 memory card so I can’t go that route to get my machine back to the way it was before. It is now very slow and frustrating to use and am considering replacing it.
Does anyone have any thoughts or ideas as to what I can try at this point? The computer is three years old and still work fine for my needs but only if I can get 512mbytes of RAM in it.

Thanks for ANY ideas or thoughts on this.

Mike