Team Explorer can connect and shows the server and projects. Source Control Explorer shows the source files and the state of check in/out. But in Solution Explorer, there is nothing! The red check marks are gone, the blue locks are gone. Right click a solution or project or file and there are no source control options.
When you try to connect to the TFS server and its offline then if you choose to still work on the solution you must eventually “Go Online” by right clicking the solution name in the Solution Explorer and select “Go Online”.
Change Source Control prompts: "The current solution is associated with source control but is offline. Would you like to completely disassociate the solution from source control?" , because you did not perform the go online in Source Explorer.
When you right click the solution name in the Source Explore, can you select Go Online item? If you can, you can perform such as the check in/out operations.
Offline means if you cannot connect the TFS Server, you can also edit your solution, and when you connect the TFS Server, you can go online and perform the check in /check out.
There is a video about work offline with TFS, you can see: http://msdn.microsoft.com/en-us/vstudio/bb898913.aspx
For more information, you can refer to