"not responding"

[julie]

I am not sure if its a problem with my windows xp
professional or a problem with my computer,but recently my
computer started to freeze after about 15 min of
use.nothing works(mouse or keyboard)and I also can hear a
clicking noise inside the computer right before it
freezes.On a couple occasions it said "not responding"on
the top of the screen but the only way to fix it when it
happens is by restarting the computer.