Well for starters what I would do is remove any expansion cards, (video cards, sound cards, etc) and also remove both sticks of memory unplug all your ide devices. Try powering it on then and listen to hear if it will beep any and if it doesn't it could be one of three things. Possibly it could be shorting out somewhere on the case, or you may have gotten a bad cpu, or you may have a bad motherboard. To eliminate the case of a short you will need to remove the motherboard and place it on a non conductive surface along with the power supply and power switch and try powering it on that way and listen to see it will beep at all. If it doesn't then likely your mobo or cpu is bad. You will have to try the cpu in a known good mobo to know if it is your mobo or your cpu.
On the other hand if it does beep turn it off then start by adding your video card, power it on it again if you hear it start beeping then power it off and add in one stick of the memory. If when you power it on it still doesn't post power it off and remove the memory and try the other stick. If after this it still doesn't post you may have bad memory or that brand may not be compatible with you mobo.
It can be a pain in arse to trace down problems like this. All you can do is go through the process of elimination. Hopefully this will help you out some to find you problem.