Before you resort to buying another Nintendo 64 system, I would try cleaning your current system and games. Random resets and crashes can be caused by dirty or dusty contacts. Take a cotton swab and dip it into some surgical spirit (AKA rubbing alcohol or isopropyl alcohol), then pat it with a tissue so it isn't dripping wet. Gently rub the surface of the cartridge connectors on both sides, then use the dry end of the cotton swap to dry the connector. Wait at least 30 minutes before inserting the game into the system. To clean the system, get a new, unused toothbrush and dip it into surgical spirit. Gently scrub inside of the cartridge slot and in between the pins. Use a tissue to pat dry the slot, being careful to not tear the tissue on the pins. Wait 30 minutes before inserting a cartridge.