Okay, I think the best way for me to convey this issue is give the current symptoms I've isolated on my own, then explain the circumstances afterward.

I have 4 memory slots.  DIMM 1 and DIMM 3 are functioning, by all accounts, normally.  Using any RAM in DIMM 2 will cause a diagnostic beep of 1 Long and 2 Short beeps and will fail to boot.  This is whether the memory in DIMM 2 is isolated or in any combination with RAM in any other DIMM slots.  DIMM 4 fails to show any RAM present in the slot, but will allow you to boot, so long as it is combined with functional RAM in DIMM 1 or 3.  Otherwise, it fails as though no RAM were present.

I think that pretty well describes the symptoms.  Now the circumstances: I bought 4 new sticks of RAM about a week ago, all identical 1GB Centon DDR2.  I had no difficulty installing them and the system ran perfectly well until tonight.  During a routine video viewing, I got a blue screen of death - IRQ Not Less Than or Equal or whatever it may be.  No big deal, I simply rebooted - well, no I didn't.  The system wouldn't post at all (no beeps whatsoever), in fact.  So, I reseated all the RAM, cleared the CMOS by removing the battery, then rebooted.  That's when I discovered the first post error (1 Long, 2 Short beeps) and began isolating the issue.  I can get the system to boot now with RAM installed on DIMMs 1 and 3 and it seems to be functioning normally.

So, the obvious question: what the heck happened to the other slots?  Is there any way to repair this?  I should note that I've also attempted to reinstall my old RAM in these slots to no avail.

Anyone have any insight?