Not so random boot problem

I recently built a box (config below) and have an interesting boot failure. I've seen others with similar problem whereby one boots but stalls before video powerup. All is well after hitting reset. I intially thought it was random, but I discovered last night that there is nothing random about it. It is a time issue. If I shut down from windows but hit the power button within 1 minute it works 100% of the time. If I wait 1 min and 15 sec it boots about 50% of the time, if I wait for 1min 30 sec it works 25% of the time and if I wait for 2 min or more, it never boots without hitting reset. It sounds like a voltage leak somewhere??? Is there a motherboard guru out there who can interpret this and how to fix it?
Thanks
My hardare is:
K8N Neo2 motherboard
AMD 64 3500+
WD raptor SATA HD
GeForce 6600 GT
Corsair RAM 1024 MB 3200XL
Thermaltake 400watt PSU