Assuming the speaker is properly connected to the motherboard, no beep means the POST did not run. A bad video card or bad memory would still generate a beep pattern indicating video or memory problems.
(You should become familiar with the POST codes. Your motherboard manual may list them. If not, google something like "asus post codes".)
If so, six possibilities:
1. The motherboard is improperly installed in the case, shorting something out.
2. Bad PSU. A working PSU will send a control signal call "PSGood" to the motherboard. The motherboard needs this signal before the CPU can start the boot process. A problem with any output should kill the PSGood signal.
3. A bad drive or video card affecting the PSU.
4. Bad memory.
5. Bad CPU.
6. Bad motherboard.
Disassemble everything. Breadboard (assemble the components outside the case on an insulated surface) the PSU, motherboard and speaker, and CPU and HSF. If the problem was in the CPU socketing, reinstalling the CPU should solve it. Now you need a way to turn on the computer. I use wiring, switches , and LED's scavenged from and old case.
Turn on the computer. If you hear beeps, the computer at least started POSTing and the PSU, motherboard, and CPU are probably good. No beeps means that at least one of the three are bad. At that point, all you can do is test the parts by substitution.
If you heard beeps, install memory and video card and plug in the monitor. Turn on the computer. No beeps now means that either the memory or video card is bad. Test by sustitution. At this point you should see something on the monitor if the video card is good.
At this point, you should see a "missing keyboard" error. Turn off the PSU and plug in a keyboard.
Turn on computer. Enter the BIOS to set date and time and verify the amount of memory present. If you can do this, it means that all the expensive parts are probably good.
Start plugging in the rest of the components and test. No beep, and you have found the problem. If everything works, it probably means that something was improperly installed in the case.
Reassemble in the case and test. If you are lucky, everything works.
I always breadboard a new build. I pretty much reserve the fourth port of my KVM switch for system testing.