so first of all i take it you are using a wirless adapter that plugs in via a usb port. i also had the same sort of problem for ages till i figured it out. First of all if your wireless router came with an installation disk run that other wise your adapter will not do much at all second of all if you have set a password try changing it with the software that comes with the disk. if this does not help i would then recommend into a computer store and asking them what they think the problem is and who knows they might be able to fix it and not cost you a cent but i hope this helps (it might also have something to do with your virus protection software try disabelling your firewall)
Josh
October 2010