Let's look at the path:
Start with a known good monitor.
Clean the memory with an eracer. Install one stick in the proper slot (check your manual).
Plug the power suppy back in ,and try it.
If there's still no video, Reset the BIOS, and try it again.
If there's still no video, Try a different video card.
On two dell T3400, I have seen this problem and found the mother board to be bad.
This problem starts with the North Bridge getting adnormally hot.
If you see this, order a mother board, you are about to loose your video.
There is a possability that the CPU is bad. Pentium 4s and old AMDs are bad about this.