What do you mean when you say you are having trouble getting your computer booting? is it not posting? not loading windows? If you can still get to your bios then go there and make sure that the ram voltage and timings are set correctly for your new ram. If you can't get to your bios then put your old ram back in, load the bios, change the settings for the new ram, and then put the new ram in.
Not at all. You can safely change the ram timings using the old ram because they are looser timings then your new ram and both run at the same voltage, so even if the new ram still doesn't work the old one will. Also if for some reason neither ram works after changing the bios setting you can simply reset the CMOS and it will restore the bios to defaults.
Hope this helps
i have a m2n-e totally evil. i have the bios fully updated and everything i have to underclock the ram(ddr2 800 from patriot 2 X 1gb) to 400(i think) and remove one of the sticks to get it to post even then cpu-z reports it running at 263.7 mhz. .
the sad part my parents bought me a 4870 for my birthday its like using a original da vinci painting as toilet tissue.