After successful ReSharper 8.x installation:
- all ReSharper menu items in VS top menu are disabled;
- there is no Error Stripe near vertical scroll bar;
- No IntelliSense;
- there are no ReSharper highlightings/quickfixes/context actions in Text Editor;
- ReSharper items are missing in contextual menu;
- When you try to clear ReSharper caches, it says "Clear Cache is applicable when solution exists only. Open a solution first.", but the solution is open.
It might be related to older version of Nuget Package Manager installed to Visual Studio 2010.
Open Tools | Extension Manager | Updates | Check updates for Nuget Package Manager | Install the latest one