sounds like it could be your battery. even though you have enough power for your accessories, it doesn't mean there is enough to crank the engine. the jeep batteries are notorius for only lasting 3 years or so. leave the jeep sit overnight then pull the battery and take it to have it tested(autozone, advance, etc). don't drive there and have them come out.
2006 Grand Cherokee Limited-5.7L Hemi-Brute Force CAI-Magnaflow 22" Muffler-Diablosport Predator-SRT8 Rear Sway Bar-Bilsteins-Shorty Billet Antenna-Chrome Turn Signals-Chrome Tow Hooks-Roof Rack-SS Ultras Highs/Lows/Fogs-Commander Shift Knob-20% Tint