Installing Different DDR Rams on the Same Motherboard

Hi guys. I have a problem with the ram, but it's a long story so please bear with me.

I recently bought a new ASUS S-presso that came with 512mb of PC3200 ram. Since it had a free ram slot, I thought maybe I could install an old 256mb PC2700 to boost memory capacity. I knew that the motherboard supports both types, but I didn't know if it could support both at the same time. Anyway, I tried it thinking that in the worst case that it doesn't work I'll just remove the 256mb.

But it did work, and my computer reported 768mb of ram at 320 MHz, which was what I expected. However, last night I turned off my computer and this morning the computer beeps when I tried to turn it back on. The beeps mean that there's bad or no ram chips found. So I tried removing the 256mb, then replacing the 512mb with the 256mb, but neither case worked and the computer still thinks there's no ram. Then I tried a different 256mb PC2700 ram (a third one) and now my computer's working off that.

I tried the busted 256mb PC2700 ram on my brother's computer, and it reported 768 mb of ram at startup, then reboots by itself, and the cycle continues. I suspect that somehow, although I thought this was impossible, the computer thinks that the 256mb ram chip is now a 768mb chip. Thinking back, I remember going on to crucial.com to do a memory scan, and it reported me having a 768 ram chip with my second memory slot empty. Could the computer have associated the 512 mb of PC3200 ram to the first slot and somehow screwed up both ram chips? Are these damages too fargone for repair? Any help or opinion would be appreciated.

Also, now working with the single 256mb PC2700 ram, my computer keeps saying something about overclocking failure at startup. I think it's because the computer usually runs at 800 MHz FSB but now it's trying to run at 533 MHz to accomodate the PC2700 ram. But that's just my guess.

Thanks

Dave