Couldn’t connect my wifi with my Macbook?

Hi there,
I'm using Macbook 2.0 GHz Intel Core2 Duo. I’ve a small office where I have a wifi setup with microtech router. My problem is I cannot connect with my wifi connection. It happens recently. I have tried several time to solve this problem but failed. I’ve restarted my macbook and also configure my microtech router but there was no progress. I faced this problem two days ago, before two days it was fine and could able to work with it smoothly. It just happened. Don’t know what to do.
Please some body gives me any solutions. I'm in great trouble. I can't able to communicate with my valued byres.
Cheers
Rubayeet
