Xbox live through pc?

For 2 years I have had my pc connected by wireless router, with an Ethernet cable to my xbox to play games online, it worked fine. recently i had trouble connecting to xbox live and occasionally to the pc at all. I reformatted my pc as it needed doing anyway. Now however they won't connect at all even as a network to watch films on my pc on my xbox. All I have done is shared the internet connection as i did before.

DHCP is enabled on the wireless router to my pc, also i have tried using static ip to no avail. Also my wireless card and ethernet card have different ip's when running "ipconfig" is this normal? I thought there used to be just one ip for the whole pc

Thanks for any help. P.s. my xbox works directly attached to the modem by ethernet so i belive its my pc where the problem lie's.