problem with xbox 360 connection

Hi there.
i used to have an xbox 360 arcade untill it got the RROD =[
so today i decided to go out and buy the new xbox 360 slim.
everything is fine, connected to the wireless internet using built in device...
and then it came to connecting to the Windows Media Center.
i go through the process.. put in the 8 digit code.... and it just says "Cannot detect extender"
i dont understand this problem as i was able to connect my arcade before.....
any ideas on the problem?

Also... my xbox shows as a device that can be shared with... yet i can't use the extender or access my computer using my xbox =/

i appologise about many another post even though there are many before it... i cannot find the answer to my problem.