2000 Jeep Cherokee HIGH OIL PRESSURE GAUGE & HIGH TEMP

I BOUGHT A CHEROKEE, USED, WHEN I FIRST PURCHASED THE VEHICLE THE OIL PRESSURE GAUGE WOULD DROP DOWN TO ZERO WHEN I CAME TO A COMPLETE STOP AT STOP LIGHTS THEN GO BACK UP TO NORMAL WHEN DRIVING. RECENTLY, THE GAUGE HAS SHOT ALL THE WAY TO THE OPPOSITE SPECTRUM AND IS SHOWING HIGH OIL PRESSURE. IN ADDITION, THE CHECK ENGINE LIGHT HAS COME ON AND THE CHECK GAUGES LIGHT HAS COME ON AND THE COOLANT GAUGE HAS ALSO GONE ALL THE WAY UP. WHAT COULD THE PROBLEM BE?