I have a 600w Seasonic that has 4 connectors that can plug into my DFI mobo. There's a 24 pin, a P4 4 pin, a regular 4 pin molex, and a small white 4 pin. I've been testing an Antec 300w PSU on this board to try and figure out why the computer won't work, but there's no output from the video card. Am I just not giving it enough power or are those other connectors necessary? Thanks!

You need to supply full specs in order to get help here.
MB?
CPU?
Video?
RAD?
etc.
These guys are good here if you give them all the info up front.

Well, it's a 300watt PSU, couldn't have very good amps on it. I'd agree with RedRaider_gamer - give us some system specs. You begin mentioning about the Seasonic but you jump right into talking about the Antec. What is it exactly that you want to know?

If you are confused about the various ATX connectors than take a look at this:

http://www.playtool.com/pages/psuc [...] #atxmain20

Here are the specs:

AMD64 3200+ 2.0GHz single core
DFI Ultra-D LanParty non-SLI
Seasonic 600w power supply
2 320GB Western Digital hard drives in RAID mirror
ATI x800xl 256MB video card
2GB OCZ 3200 RAM 2x1GB
Antec P180
Linksys 802.11g WiFi PCI card

I tried the Seasonic on my other P3 1GHz computer and it wouldn't boot up either. Then I went and bought a temp 600w CoolerMaster PSU from CompUSSR, and now the system works perfectly! Also the specs for the motherboard say it requires something like a 480w PSU. Apparently all 4 connectors should be plugged in as well.

That mother had to come with a booklet showing you how to hook things up. If it didn't, goto the manufacturers site and find out how to do it right.

that display card have another power jack ?