System Beep Problem in Compaq Deskpro P3

Hello!
I need some help regarding my Compaq Deskpro 500 Mhz on P-II Motherboard. The problem is that when i hold any key and then move my mouse, system speaker starts beeping and system starts hanging for a short time.

Now when i disable PC Speakers from the Volume Control Panel, and do the same process again then we get rid of beeps but the system still hangs for short time. I am using Windows XP Pro and Windows Me but the problem is in both OS.

I have tried many times to disbale my built-in sound card but its for no use. Please advice me.

Thanks.