If these are the gauges you're talking about:
RoF simple gauges 1.jpg 182.05KB
Then you need to go into the mission settings ("realism") screen and tick the simple gauges box, as noted below:
RoF simple gauges 2.jpg 209.21KB
Once you have them ticked, you can then toggle them on and off with the CTRL+I combination (assuming you haven't changed it from default).
However, I would strongly recommend that you not get used to using these aids - it is so much more immersive and satisfying (IMHO) to get all this same info using the working instruments on the plane itself.