Home & Small Office Network

Firstly apologies if I am posting this on to the wrong Newsgroup, but it
just seemed to logically be the right one.

Our small office has 5 PC in it all with shared folders under one
workgroup and all working fine (all PC's are XP Home, except one which is
Win98SE). We replaced the ethernet cable with USB wireless adapters and
plugged an access point into the wall port. All can see the router
through the access point, all get allocated IP addresses and all can see
the internet. But now the file sharing doesn't work? We get a message
saying the workgroup is not available and to consult your network manager?
I know this is a bit vague, but any ideas from anyone would be greatly
appreciated.

Thanks to all
Jason