Win7 volume control icon turns gray solution

The inexplicable Win7 bottom right corner volume control icon is gone, you can release the sound, you can adjust the volume in the control panel's adjustment system volume, check that the sound card driver is also correct. In the system control icon, the volume column is gray (as shown below), can't be changed, what should I do?

1. Open the program manager (ctrl+alt+delete)
2. Find the "explorer.exe" in the process, and then press the end process (the toolbar will disappear)
3. Then in the file (upper left corner of the program manager), click "New Task"
4. Then "Browse"
5. In the c:/windows/system32 folder, find "systray.exe" and then click "OK"
6. Once again, open the file, new task, In the blank bar: explorer.exe, OK
7. The icon will be displayed.
Note: Sometimes the problem will still exist after the restart, or the file systray, exe can not be found, in fact, WIN7 SP0 One of the bugs, if you can't stand this phenomenon, you can use other versions of Win7 to reinstall.