Unstable Internet Connection When Changing From Cable To Wireless?

I have this problem with my laptop. If i am using a cable to connect to the internet and then unplug it and switch to wireless connection, the internet connection gets unstable. The thing is it says it is connected to the right wireless connection AND it claims to have internet connection. - And i do - for a few minutes.. If i deactivate/activate the wireless internet i am able to surf around for a few minutes again, but then it does the same thing again - shows up as having internet connection but im unable to connect to it..Strangest thing is that i am sometimes able to connect to the internet ONLY if another computer is using the wireless internet too.. It still shows up as recieving a nice signal with internet access even though i cant connect to the internet.

The same problem also occurs sometimes when im switching from one wireless connection (at home etc) to another (work etc)..I've had this problem for a few months now.. Comming to think of it i might have had this problem ever since i got my laptop.. Rebooting my computer fixes it every time, but it's not a permanent solution.. Im running original Windows 7 Home Premium x64 which came with the laptop.. Also im not using static ip or anything like that - switching to static ip doesn't do the trick.. Running ipconfig /all command from cmd also shows me as connected to the right router.. The problem occurs every time i switch between cable and wireless and not only at my home or work but also at friends..I'm not sure if i need to leave any more details, if i've left anything out just let me know.