new build (IC7, 3.2P4, Corsair XMS) not posting, sometimes

This is weird. I just got my RAM and CPU to upgrade my #2 rig. I first installed the RAM in dimms 1 and 3. Intalled the CPU. It booted up, I went into the bios to check the settings. I noticed the temp was 48 idle, as hit 51 after 5 mins, so I shut it down to chech that the HSF was mounted right, it was, so I tried booting again. Nothing but a black screen. So i tried different configs with my old and new CPU's and RAM. Sometimes it would boot and sometimes not. Now the only way it works with the P4 is with one stick of RAM in dimm 4. The only way it will work with the Celly is with one stick in dimm 2. And that is with my old el cheapo RAM, the Corsair wont work.

Any idea on what the problem is?

Any and all help would be appreciated. I need to find out whats wrong so I have time to RMA something if need be. I havent even been able to OC yet.

so slots 2 & 4 are causing you problems?

You cleared the Cmos? You test each stick individually? Everything is hooked up properly and double checked? You have the latest BIOS flashed? 48C for a Prescott in BIOS is not very hot, that doesn't supprise me at all unless it's a NW core. Tried booting without anything other than mobo/cpu/mem?

Slots 1 and 3 never work. (I used slot 1 before the upgrade) Slot 2 OR 4 will work, but never together, and only if paired with the CPUs the way I said in the first post.
I have cleared the CMOS after every failed attempt, before trying something new. I tested every stick individually, in every combination. (That took a while!) Everything is hooked up right. The CPU is a Preshott, my Celly idles at 44, so I shouldnt have been to shocked. But the temp seemed to be rising too fast, since it didnt even have a load on it.
I havent updated the BIOS from where it was when I got it, technically. Actually I did update maybe a month ago, but it acted really weird so I reverted it to the original. I still have the file so I will try it again.
I havent tried it with only CPU/RAM/mobo, I should do that then too. So even take the vid card out?

Thanks for the input Kevin007 and Sucka, I updated the BIOS and everything is fine. Except that when I go into the BIOS and change something, then try to "Save & Exit", it wont accept any keyboard commands. I've tried a couple different keyboards so that's not the problem. And it is fine if I choose "Exit Without Saving". I just d/l'd the latest BIOS again and will see what happens.