I've had similar problems, partly solved by me, and partly solved at great cost by a chap from the local computer shop.
Things to watch out for that I got wrong...
(1) Don't have more than one way of connecting at a time, disable all but one. For example, don't have a hard-wired AND wireless connection to the router on the same PC, it'll tie itself in knots.
(2) Watch out for firewall software, it can decide that the wireless network isn't secure enough for it's taste and stop you accessing it.
(3) Check all the right bits were installed as part of Windows. You might need to do an update installation.
Failing that, call in the local computer shop!
G
Glad I'm only paid to understand aeroplanes.