I had an annoying problem in Visual Studio 2008 that cost me about 3 hours of time. I was working in C# and noticed that my IntelliSense had ceased to work. I went into the options under C# and sure enough IntelliSense was still checked; so I removed the checks, hit OK, restarted Visual Studio, came back in and turned IntelliSense back on. However. It still did not work.
3 hours later, I found the source of my problem. The “Auto list members” check box was no longer checked, thus disabling IntelliSense. This was obscure because one would have thought something with this much control over IntelliSense would have actually been on the IntelliSense settings form but, either way, it fixed the problem as soon as I added the check back.
So if your IntelliSense stops working, make sure you have the “Auto list members” box selected.
1.Goto Tools | Options
5.Check ‘Auto list members’