All of the parts are known to be working and the pc was working before switches.

MotherBoard is a K8V Deluxe
AMD Athlon 3000+
PowerSupply 550W (it previously powered a X19050Pro 256

As of right now, all fans turn on (including the video cards) on boot up, but no output to the monitor. Only the video card, 1 stick of ram (512), 2 case fans and processor are currently plugged in. It does not make any beeping noises.

I believe connections to be good ( such as power and reset button connections) as they were working before and I did not change them.

Earlier the pc would not start. Only flutter once when I hit the power button ( attempted several times).I unplugged everything and powered on. It powered on (fans) and I heard a pop noise (sounded came from an unplugged power plug, I believe) I then plugged in a 9800 pro, but its fan did not come on (not enough power, I assume) . I tested on several of the power plugs to no avail. Switched to GeForce 2 ( doesn't require power plug in) and its fan turned on. The power plugs that could not power the 9800 pro do power the case fans.

This problem arose because I did some part swapping between this pc and another.

Thanks for any help

Did you move the Motherboard to another Case? If so, doublecheck that there are no Spacers underneath in the wrong position that may be shorting the board to the Case.

Have you tried a known working PSU? Often the fans will spin, the HDD powers up, but one of the other rails has blown -i.e RAM or CPU getting no juice. Seeing as you have no BEEP, this sounds likely

Motherboard is still in same case

I did change the power supply (550 to 300)

Unfortunately, the problem still exist.

I did not mention before, but the green light on the motherboard is on when plugged in.

It should be...

Can you pinch some RAM from another PC and try that?

I switched to a different (but much older motherboard) and the PC is up and running.

If it proves too dated, I will try a RAM switch, though I am fairly sure the RAM is in working order.

Thanks for your help