Dimension 4700 Wont Boot After Installing 8600gt

I'm a little baffled on what's going on and hoping someone can shed some light... I bought a couple things for xmas to upgrade my little brothers PC and everything works fine except for the video card I bought him. I had installed 2gbs of ram and a new power supply to work with the video card however when I put in the card the computer turns on but nothing loads up. There's no beeps and the monitor doesnt even turn on.

I put the card into my pc just to make sure it wasnt the card and it works fine for my pc so the card checks out.

The video card is a EVGA 8600gt 256mb ddr3 and the power supply is 500w which i think is plenty for this card.

Basic specs for the pc are 2.8ghz, 3gb ram
And the power supply is a APEVIA ATX-CW500WP4 i believe 12v1 -16a and 12v2 - 18a.

do the fans spin up, are all the power cables connected, is there power going to the video card

Yeah, the fan spins up at full speed and all drives and lights turn on. This card doesnt have a separate power plug so I'm hoping it's drawing enough power from the mobo.

if you take the ram out does it beep

Ram issue, either incompatible or the 2GB issue.
Is the ram same speed, voltage, timings, ecc or non-ecc?

Read your manual:
http://support.dell.com/support/edocs/systems/dim4700/sm/specs.htm#wp1043338

8600GT only needs 300@18amps (no extra power connection needed) so even that weak psu should be able to handle it)

Yep RAM

yeah sounds like RAM to me, but sometimes a bad post problem can be caused by a power supply (usually the 4pin for the CPU is faulty) If you hold the front button for 10 secs does it shut down? If it does its the RAM, if not its the CPU/Powersupply