I am writing apex class in developer console in salesforce but it cannot save in my salesforce account. Help me in this regard
This appears to be an infrequently encountered but annoying bug within the product - or at least other people are seeing the same problem: https://success.salesforce.com/ideaView?id=08730000000jhavAAA
Have you tried using MavensMate as an editor instead of the developer console?
I recommend never using the online editor for your salesforce code. You are really limiting yourself by not using a real IDE such as Eclipse or MavensMate.
Eclipse isntallation instructions: https://developer.salesforce.com/page/Force.com_IDE_Installation
I'm not as familiar with setting up MavensMate but I do know lots of people have had success with it.
That said, you definitely need more detail in your question other than saying it's not working.