If the beeping noise occurs during startup, before you hear the standard POST beep (1 short beep), it is an error your could motherboard is giving you because there is something wrong with the boot sequence.
My guess is simply that a wire has come off (especially if you're using SATA) so you should go into your case and make sure everything is connected securely, but you should check your motherboard manual for the beep codes for identifying the problem.
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w