Although I don't think I completely understand your situation, it sounds to me like you have a combination of problems. The first of which possibly being bad RAM.
The second part of your post seems to indicate you installed another two sticks of memory; one of these could be the problem or perhaps when you were installing the hard drives you knocked an existing stick out of alignment. I'm sure I don't need to tell you that bad memory is going to be writing corrupt data to your hard drive which could make it seem that the hard drive is at fault.
First port of call would be to re-seat all sticks and conduct some tests on the memory to check they all work OK.
But I guess you've already looked into that?
The second problem I can see is that you ever trusted Partition Magic to do anything. I've heard a lot of bad things about it over the years and I suspect it's still not a very safe bit of software. Stick with the default Windows partition manager next time.
You could try the following boot disk to check the drives without installing anything:
http://www.ultimatebootcd.com/index.html
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