VS2005, XPSP2, 2Gb Ram

When working on the default.aspx in a web app intellisense intermittently
stops working
Also If i do a build the build succeeds even when there are major errors
such as absurd class names, and incomplete statements. when I run the app I
then get a compile error as it tries to load.

On one occaision I have fixed this by excluding this page from the project
and then re - including it, but this does not always work.

any ideas?

guy