New PC ram question

I finished building my new PC a few months ago. When I originally created the list of items I needed I was originally going to go with the sandybridge setup. So I only got a pair of 8gig dual channel ram sticks. when it got recalled I decided to just go with a i7 960 on a tri channel Mobo. That being said I had to buy an extra ram stick in order to have tri-channel ram.

The problem is i didnt realize this one ram stick had a different memory timing that the other two. The first two are 9-9-9-24 and the last one is 7-8-7-20. I also noticed that when originally built it registered all 12 gigs of ram but yesterday i noticed it only registered 8 and it seems that it's not registering one of the 9-9-9-24's.

Now for the question: I'm wondering if me putting to different timed rams in at the same time may have burnt one of them out? Or does that not matter at all and I just have a bad stick?

It's high very unlikely one of your sticks will "burn out" and it's even more unlikely that the computer would boot with bad ram.

Brand and model of the mobo will help us giving a better answer.

For now you can try to boot with each stick and then add all 3 again.
It can sometimes solve the problem.

First thing to do would be to run Memtest. Then try to boot with each individual stick by itself. If it doesn't boot with one of them, either that DIMM or the slot itself is bad.

As an aside, unless something has changed recently, mixing 'n' matching RAM sticks is fine, albeit counterproductive. All sticks will run at the speed of the slowest stick and, obviously, you won't get dual/tri channel mode - for that, the RAM sticks need to be identical.

As usual, I may be talking out of my arse, but I don't think so this time ^__^

As long as you fill all channels with a equal amount of memory tri/dual channel will kick in.