iPhone 2g says it has no wifi, how do I fix that?

The person who I bought it from said he replaced the back cover and motherboard and everything was perfect until like a few days before he sold it, he said that the wi-fi just stopped working.

Anything I can do to repair it ?

*Since the cover is not from the original phone, and neither is the motherboard, the model listed to the right might not be accurate, because the motherboard is a 4gig and the cover says 8gig on it.