fallout 3 problem

so im playing fallout 3 on my pc as i saw that the ps3 version isnt that visually nice. my gfx card can handle it to high without lag and sometimes even ultra high with some lowered settings between high and ultra.

but the thing is it always lag even when it is on low settings and sometimes it stucks and i hear a beep from the cpu and then it comes normal again:

MY PC:

AMD Dual Core 3800+

XFX Nvidia 7600gt xxx (its not the gfx the problem im sure)

Asus Nvidia NF630i mobo

3GB 667 DDR2 RAM

Seagate 160GB IDE 5400rpm

what do oyu think is the problem my bet is the cpu. im asking here cause i dont know much about pcs. thanks in advance guys

Obviously something is wrong, your PC shouldn't be *beeping* at you. It wouldn't be your CPU hat beeps, it would be your motherboard. Most likely some type of hardware problem, but without being able to trouble shoot the problem myself, I wouldn't know what the issue would be. It could be a number of things...PSU failing....GPU over heating (though this generally causes your system to shut off or lock up)...maybe you have a faulty stick of RAM? I'm sure there could be other reasons, but those are the only ones that pop in my head at the moment.