CPU Upgrade Dimension 9100

Hello all, a little help if you would.

I have a dimension 9100 with a Pentium D 830 cpu inside, eating a lot of electricity. Having done a little research, it seems that the intel 945 chipset that adorns my motherboard should be compatible with the far newer, more powerful and more power efficient pentium dual core series.

I made sure that my BIOS was updated to the most recent version, A03, dated sometime in 2006. So i ordered myself a Pentium dual core E5400, popped it in and nothing. Which was annoying. (power light on front stayed orange after pressing, HDD spun up as did all fans, but not graphics card.

As such, my question is, is there any reasonably recent CPU i can upgrade to which will be more powerful and more power efficient than my 830? (i plan to buy a shiny new core i7 pc in october, but until then, need a little more grunt.

Thanks in advance.