Not always.
I had a thread about this not too long ago, and some mobos beep, others do not. Friend of mine has had three machines in a row over the years (a Dell and two eMachines) and none beeped after a POST. Both of my pc's, ( a DEC and an eMachines) beep after a POST.
Do you get fans spinning? Does your floppy grind away looking for a boot disk? Do you get anything at all on the monitor screen? Is your monitor the same one you used in the past?
Triple-check all your cables inside. Re-seat all your cards. I had this happen to me once and I'd forgotten to seat the auxiliary CPU power connector.
Tom