slow PC

Hi everybody.
I wanted to ask for your grateful help with a problem i have.

i replaced CPU,motherboard and RAM in my father's PC.

the PC was very old and slow so i bought new i3.
of course i installed a fresh new win 7 after the hardware upgrade,
and i made all the driver updates. after that the PC is still slow,
better then what it was but still not what i was expected for.

wish for your help.
thanks ahead.