The problem is your graphics driver appears not to be loaded so your PC is running at default settings which are very low res and minimal colours.
You monitor may also be running on default VGA settings as it may not have detected the make/model or loaded the drivers properly.
If you right click on the desktop, press properties then settings, you should see the monitor make/model, the graphics adapter name, plus the resolution and colours that are being displayed "IF" the graphics adaper drivers are loaded properly and the monitor has been recognised correctly.
Martin
Replying helps further our knowledge, without comment leaves us wondering.