Dimension E520 PCI-E graphics card..HELP!!!

Ok, so a few years ago i tried replacing the stock ATI X1300Pro with a HD2600. At the time this didn't work (no video), so i just gave up...

Today, having forgot about all that, i receive a new ATI HD4670 card which only pulls power off the PCI-E socket. Anyway, i plug it in and......nothing, no video what so ever. Front panel lights 2 and 4 light up to show graphics card error..doesn't POST etc etc

So, where am i going wrong here?

Card is installed correctly, and i know the card works in other machines - why the heck wont anything other than the X1300 work in my machine!!!!

Is there some BIOS setting or Mobo jumper setting that needs fiddling with?...Is the 305W PSU not man enough to power the card (when connected the fan on the gfx card runs).

I've seen similar stories on the internet but never a resolution...So come on guys (and gals)...what do i need to do from here!

Other hardware is Intel Core2 E6600, 3Gb ram, 2x HD's, 2xDVD, soundblaster card..thats about it

Proper doing my head in this!!