New MoBo, old PS, won't boot

Just built new system with ASUS P5KPL-AM SE, Intel Core2Duo, WD 500 g SATA HDD, LG DVD-RW, 4 g SLI 800 MHz RAM, 5 case fans (80 mm) and a 400W ATX PSU using a 20 pin connector. All PS connections completed (including the 4 pin CPU plug). Power on produces LED on board, LED on HDD, all fans running, and blinking cursor below the Intel disclaimer. Can't complete POST or get to BIOS to configure hardware. CPU is cold and RAM barely warm. My guess is the PSU can't provide sufficient to power the system, especially without the added 12V rails. Would this be an accurate conclusion?
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  1. Best answer
    A working 400W psu will power any system not using a video card. So unless you forgot to list your vid card, that's not the issue. 20 and 4 pin should work instead of 24 and 8 pin.

    When was the last time this psu powered anything? Can you put it back and see that it still works in the old system?

    - Try booting with just one stick of memory . . . then try with the other. If it fails to boot with either . . .
    - Pull power/data from the HD & DVD and remove all memory. Power up. Does it power up? What do you hear from your onboard speaker?
  2. I can almost guarantee that the mobo requires a 24-pin connector, in addition to the 4 pin CPU plug. It may not allow POST without it.

    But that's just what I think, if anyone else has any info on it, feel free to correct me. I'm always up for learning something new.
  3. My quess would be PSU even though I have successfully ran a modern 24pin mobo on a 20 pin psu.
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