Memory, DIMM slot, or Mobo issue?

I think I finally found a forum that might be able ot help me. I have a computer with and MSI K9AGM motherboard and originally had 2 1GB sticks of Crucial DDR2 6400 (800Mhz) 2.0V memory sticks in it. I went and bought 2 1GB sticks of Kingston DDR2 6400 (800Mhz) 1.8V sticks and added them. I understand it wasn't a good idea to mix and match but here is my problem.

I have 4 DIMM memory slots. Oringinally the Crucial memory was in DIMM slot 1 and 2 and the computer recognized 2GB of memory. Now when I added the other two sticks of Kingston so all 4 slots are filled the computer only recognizes 1GB of memory (and after doing some troubleshooting) I discovered the only slot that works is the 4th DIMM slot. The other 3 slots do not recognize the memory and if I boot up the computer with nothing in the 4th slot the computer and fans fire up but nothing on the screen and no beeps. Even when I took all the memory out and tried to go back to my original setup that recognized 2GB of RAM it does not work anymore. I tried each individual stick in DIMM slot 4 and the computer started up with each stick which leads me to believe the memory is fine. Any other combination the computer will not boot up if there is not a stick in DIMM slot 4.

I am at a complete loss. Did my 3 other DIMM memory slots go bad? Would of been a weird coincidence. I don't know what to do and was hoping I would not have to go get a new mobo. If I could get the other slots to work I would toss the Crucial memory and go buy 2 more GB f the Kingston so they all matched and be done with it. I haven't read anything that says I could of screwed up these DIMM slots but I truly do not know. I did update my BIOS to the latest version and loaded optimized defaults.

Any help would be appreciated. At this point I can only get my computer to work with 1GB stick in the 4th slot and they all 4 sticks work individually. None of this happened until I went to change the memory to 4 1GB sticks which should at least recognize 3.0 or 3.5GB.

Ideas? Suggestions? Or screwed up mobo?