HELP! no wireless connection!

I have a laptop with a wireless lan. It's been working fine until i was making some changes to share files with my other (desktop) PC(or that's the only thing i could think of that might've affected my laptop).

Since then, my laptop is not able to connect to the access point at all.
My laptop could pick up all the available access point(at work and also at home.....my linksys router shows full strength signal). But whenever I double click the avilable access point, those typical window pops up(which shows one computer and one machine(?) trying to connect.....green line going back and forth...) but after awhile it just disappears as if nothing had happened. It will never connect(the wireless icon on the bottom right of the screen has that RED X mark).

I was able to connected to the access point at work from someone else who had it unsecured.....and also at home with my own wireless linksys router. But can't get it to work nemore. I'm sure it's not the router cuz it's not working at home and also at work. But i've tried disabling all the security stuff(mac filtering...wep...etc) for my home's wireless router

I've looked at several threads and made sure i obtain my IP add and DNS thingy automatic...

do'nt know what to do ne more