PC 's stoppage and restarts

Hi there guys, I didn't find suitable forum section for this thread so I'm putting it here. Hope there's no problem with it.

I'm close to total mind collapse, so I'm posting this and hoping for someone's help.
Been fighting with this couple of months with no result :-/
So here we go : my "old" pc was blown up by the power supply. And because I plan to buy a whole new pc after NY 2009/2010, I've just bought some bazaar components for now (quality one, from good owner). And here have started the troubles. When I push power button (but following action appears only for the FIRST time of starting the pc, after restarts - for example because of installing the utilities, it's everything fine), pc boots, windows starts, and after few seconds my monitor goes in black and after this "black out", after few seconds pc restarts. After this restart is all fine (it's not doing that anymore). But this is repeating everytime I start the pc ... and one more information - this was doing also with 350W Eurocase power supply, and finally, the temperatures -
MB: up to 30 degrees (celsius scale)
CPU : up to 25
GPU: up to 50
HDD: up to 40

My recent pc configuration :

MSI K8T NeO2-F
AMD Athlon 64 3000+ (Venice), with Thermaltake Blue Orb II
Gainward nVidia GeForce 7600GS (AGP)
2x512MB RAM PQI (400MHz)
2x PATA harddisk (Seagate 250GB and 40GB Maxtor)
2x optical storage - DVD-RW and DVD-ROM (1 is unplugged)
Sound Blaster Audigy SE
Realtek network adapter
Seasonic 400W

Really looking forward your help community

It is power problem. Could be PSU or power circuitry on motherboard. Since it is doing the same thing with 2 PSU's it is probably motherboard. Look for bulged capacitators on m/b.

*** this isn't funny, as soon as I finnish my post the pc restarted ...