Some of the keys on my keyboard work intermittently.

Hi there,

A few days ago, i was presented with the problem of an intermittently working left shift key. The problem went away after a few days but now the D, Enter and Backspace keys are not working. I have tried cleaning under them to no avail. It may be helpful to know that they do work half of the time, and that when they stop working, they do it all at the same time I.E. When the Enter key stops working D and Backspace go too.

Thanks for the help!