Is there a difference in the freezing from when the engine is on or off? Does it freeze easier with the headlights or other accessories on? Sounds like your sound system is sucking more power from your battery at higher levels and not leaving enough for the inverter/computer. May need any of the following: A better battery, a cap or tank circuit, higher output alternator or just a better inverter or P/S.
How is your inverter wired up? Should be a high gauge wire to the battery. If you have a high draw sound system you may want to keep separate power leads for your computer and audio setup.