This is one of the problem which i have encountered personally. Whenever we install visual studio 2008 and also update it to service pack 1, we face some error which shows
"the visual studio language support for c# has not been installed. code-editinig intellisense will not be available. Markup intellisense for sever controls may not work"
By this error intellisense will not work and c# coding becomes like normal text as no intellisense support will be there. At this point of moment follow the below instructions.
Go to start-> Programs -> Microsoft visual studio 2008 -> Visual Studio Tools -> Visual studio 2008 command prompt.
In that command prompt enter "devenv/resetskippkgs" and press enter.
After doing this intellisense with c# support will work correctly.