When the PS3 turns on it says over the network I need an ip address! Your router as the
DHPC server on your network has two sets of addresses it could assign
one set which are leased and expire after a period of time
one set which are static.
It is the default for a router to assign a leased address
You need to tell you router to always assign you PS3 the same ip address
If you post the make and model of your router I'm sure we can find a guide on how to do this
On my router all I had to do to set a static ip on my server was tick a box