今天发现toolbox里没控件，提示“there are no usable controls in this group...",在网上找了些方法，发现下面这篇相对比较全。
我用show all，重启，再取消show all之后能正常显示了。
下文转至：
http://www.cnblogs.com/frischzenger/p/4504183.html
还有一些解决方案:
1) Closed all instances of VS, went to: C:\Users\Casey\AppData\Local\Microsoft\VisualStudio\10.0, and deleted thesde files:
toolbox.tbd
toolbox_reset.tbd
toolboxIndex.tbd
toolboxIndex_reset.tbd
2) In VS command promt: devenv.exe/resetsettings
3) In VS: Tools > Choose toolbox Items > .NET Framework Components > Reset
4) In the toolbox tab, right clicked and selected "Reset Toolbox"
5) In the toolbox tab, right clicked and selected "Show All". This shows a long list of tool options, but in every case they are greyed out and not usable.
5) Rebooted
6) Cast a few well chosen hexes and spells at Microsoft