Sometimes, the intellisense Feature in the Visual Studio .NET 2003/2005 Stops Working.

If you press Ctrl + Break, it will not display the Intellisense List.

This is because some of your other process is overriding the key hook. so please reboot your system in safe mode (by pressing F8 While Booting) and try.

It should work. To find out which process is doing that, use  process explorer from sysinternals.com or try to isolate the process by stopping processes one by one running.