New configuration fails at startup

Here is the configuration in question:
Processor - C2D E6850 @ 3Ghz
Ram - 2 x 2GB Corsair DDR2-6400
Motherboard - DFI Lan Party JR P45-T2RS (Micro ATX)
Hard Drive - Samsung F1 1TB
Power Supply - Seasonic S12 500W
OS - Windows Vista Pro 64 bit

The problem is that the config was installed, the system installed without a problem, then as a result I took the opportunity to re-download a few tens of GB of games that I have on steam all night. At daybreak, the PC is stuck on the first screen when boot (where the model, the amount of RAM, brand bios, etc ...). Several reboots and always the same thing it gets stuck on the same screen ...

I thought a problem of RAM so I changed with crucial Ballistix and it is always the same ... (by some miracle I managed to boot once on a slide, and the next reboot it no longer worked ..)

I thought of dirt, a mounting problem, so I disassembled everything, and reconnected back and always the same ...

I thought a problem of bios configuration, so I do a clear CMOS for everything by default and always the same ...

As a last resort, I think is a problem of power supply or motherboard. Does a Seasonic 500W power supply would be sufficient to support the configuration? For the motherboard, it is normally of high quality, and I say, if it worked yesterday and again tonight, I do not see how it could.

There is a speaker connected to the motherboard? If so, remove the ram and start. Does it beep? Maybe there is a digital display on the motherboard?

No display to what I see and I do not have the speaker.

Does the fans rotate and light up the LEDs when you turn on the computer? Also did you tried disconnecting peripherals style sata/ide?

The fans turn (once the fan of the graphics card did not work). The LEDs light up (which oddly led the standby ...)

Yes, I unplugged the power supply, removed them one-half hours and nothing has changed.

Disconnecting device type HDD, CDROM it's always the same

Try unplugging everything else, keyboard mouse etc ... , leaving just the screen, or try to test another graphics card, but it looks good the more of a problem with the motherboard