I'm using Mass Storage template of Keil5 but when I run it (on board),I can't access the SD card and PC just detects that a device is connected to USB. I commented check_media function because it's available in my board. what's wrong?
I think the correct interpretation would that no one here is providing support for it.
This, and your other post lack a lot of specificity about your board, chip, and pin usage, or software/package versions.
http://www.keil.com/forum/60249/
I would suggest you formulate your questions/queries in a much more comprehensive manner, where you have some kind of complete project that can be analyzed, reviewed and tested, and the problem(s) more clearly understood, and solvable. At the moment the issue is a bit vague, with an lot on unknown unknowns.
Finding the right engineers to provide hardware and software support can be an expensive exercise. You'll likely have to own some of your own development, integration and debugging tasks, and climb your own learning curve.
Break the project/tasks into smaller pieces, which you can test and validate individually.
ie test the SD access and functionality separate from the USB/MSD parts