Computer powers, no display, no beep

Hi. My config is: Pentium D 920 2.8 GHz stock
2x 1GB DDR2 RAM ( I 0 I 0 )
HP Customised asus mb
1x Geforce 8400GS (just solded a new capacitor on it since the older one exploded.)
300W PSU
2x DVD drives
1x HD sound card
1x TV card

Yesterday, i found out my computer just detected 1 GB of RAM. (on Windows 7) so i went in the BIOS and BIOS also detected only 1 GB. Only 1 slot. (the 3rd) so Ive opened my computer and i saw the 1st slot RAM wasnt properly seated. So i re-seated it. When i tried to power up, HDD drive works, DVD drives also, fans running at full speed, fan on the Graphic card also works, but no display and no beep. I tried try my monitor on another computer, it works. I tried to remove the 1st RAM slot, dont work either.. Any ideas? The HDD works but doesnt seek since the computer doesnt pass the POST probably.