Did you try uninstalling any Visual Studio product?
If you did:
After you install a Visual Studio SKU, you may see an error that MSVCR100.dll is missing, and other Visual Studio SKUs will fail to run.
This is by design. For pre-release versions, this will occur if you have multiple SKUs on your computer. For example, you may have installed Visual Studio 2010 Ultimate and Visual Studio Test Agent 2010 on the same computer. Uninstalling Visual Studio Team Agent will break Visual Studio 2010 Ultimate.
To resolve this issue:
1. Re-install the product that was uninstalled.
- Go to the installation location for the SKU that was uninstalled.
- Run Setup and follow the instructions.
2. Repair the broken SKU.
- Go to the installation location for the broken SKU.