I could really use some help…

I’m trying to re-build my old computer with a new…
Intel D955XBK I955X Socket 775 ATX Motherboard
Intel Pentium D 820 2.80GHz 800MHz 2MB processor         
Antec SmartPower 2.0 SP-400 400 WATT Power
1GIG DDR2 RAM
Nvydia 64mb Graphics card
(The case; hard drives & optical drives are all parts from my old setup.)
The only thing that I currently connected to the MOBO is the power source; the processor; the fan; the RAM and the video card (NONE of the drives are in any way connected) and I have already TRIED to clear the CMOS.

The problem I’ve been suffering through is that- First, the only way that I can get it to power on is by removing the onboard “coin” size battery-then keeping it out for a few seconds-then after reinstalling it-turning the power on, and BINGO it turns on!

Second, when I try to finally get in and adjust the settings in the BIOS it LOCKS up and would not allow me to go any further than a “TAB” two to the MAINTAINANCE or the to the MAIN-(when I got it to tab to the MAIN it showed that it recognized the type of primary parts of my computer…MOBO; Processor; RAM). Then after about 90 seconds the system just SHUT down. I went through the removing the battery thing and got it going again, only to have it shut down again and again…

Please help!!!
Did you use the standoffs for the MBoard when assembling ? ?
Did you remember to use thermal compound when assembling the CPU ? ?
Have you properly hooked up the mini wires to Header 1 which controls all the case switches ? ?

Is this a new PSU or a used one ? ?

On a new build you shouldn't be fooling with the BIOS at this time....use the default settings until you are up and running.