Get acees to the internet without knowing security key in window 7

why do you think it is call a "Security Key"?

http://www.tomshardware.com/forum/31382-43-find-securit...

The same way that you get money out of the bank without having an account there. Neither pastime is recommended.

If the router is yours, the instructions linked by Emerald should help you reset your security key. If the router belongs to someone else, ask their permission to use it, and for the key if their answer is "Yes."