I havent done any networking apart from USB to USB and never even looked at a wireless setup but as with most wireless applications these days,from PCs to telephones,they are frequently coming with various switches to select different channels to prevent interference from someone else in the area being on a similar frequency.
Is this so with wireless networking on the set up you are currently using?
If so have you double checked that they are on the same channel/s ?
Have you tried selecting a different frequency/channel if this is an option ?
The only other thing I can think of at this stage is contacting the wireless router suppliers helpline and seeing if they have come across this problem before