Old P3-700 RAM showing 256 but actual 512

It started lately that my P3 machine (700 mhz) displays RAM 256, but actually I know it has 512. I opened up and re-sitted the memories and swapped around but no luck. I also found CD-rom disappears as well.

This only happened after I went to a Chinese website where it automatically downloaded "Ci Ba" virus scan. That day the system hung. Ever since I had this problem. I thought the software shouldn't damage the hardware, but it seems I was wrong.

I plugged another identical CPU to the board, still the same - so I know CPU is good.

Any idea? Thanks.