I tried cleaning the slots, but it still didn't help.

Could be a CMOS issue-- ?? Mad, what do you think?

Dark -- a suggestion.

I suggest-- when you repost-- go into "My PCHF" under site navigation under "edit options" --scroll down the list.List all your hardware in the spaces-- at the top-- there is an option to "allow others to view my specs" click on yes. It saves a lot of time between posts if while you check something we can go look up your mobo manufacturer's site and read the manual.
You can also list your OS...all this is a great time-saver for us-- we can view everything quickly to refresh our memories... as we are all working multiple threads at once.This would be automatic from that point on-- so if you have another problem six months from now-- we can instantly know what you have.

My first thought was CMOS, but he said that it was working at some point. Like you said, it doesn't take much, poor contact, but this could be on the board itself. I guess an update wouldn't hurt at this point, but I can't see dark being able to fix this one without replacing the board.

Yeahh... I was hoping that it could be simple-- but probably not

Hi welcome to the forum Have you tried this the ram you know is working in the 2 slots remove it from the slots and fit the working ram into the suspect slots duz it just beep or duz it boot. If it boots your ram is faulty if it beeps your mainboard is faulty hope this clears it up for you

When you were changing the CPU fan did you earth yourself? If not you may have accidentally touched the slots and caused a transfer of static, i know this can cause damage to RAM but im not sure if it can cause damage to the memory slots..? might be the problem though