Yep - sounds like a timing problem. But then again, wrong timing usually makes it so you can't even boot to your BIOS.
I don't think its a case of the RAM being double density or anything since your BIOS would report lower amount of memory - 512 MB if it weren't able to see one side for example, and since it sees it and says its 1024 MB, then it can see whatever density it is.
You either have bum memory, the timings are wrong, or your OS coincidently got corrupted at the same time. I'd opt for bum memory.
Just my 2 cents.
-S
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