Help,got a problem

[Galhad.!??]

i have dell pc with 4GB RAM and intel core i3 2350 M CPU @2.30Ghz.
how much fps should i get?(ET)
when i play et i get unstable fps its usually 10-15 fps and i think the problem is with et
cuz i ran other games with good fps like PES 2013/2014 and CoD 4
and even with low quality cfgs it stills the same
what do you think the problem is guys?
P.S it was running normally before with a different et installation on the same pc