page contains symbols and garbage:
try reinstalling drivers.

black pages:
transfer corona wire fails to place charge on drum. In some cases, changing toner cart will fix this.

blank pages:
No toner/low toner, faulty power supply.

paper jams:
bad paper feed rollers, clutch/drive gear, damp paper if the jam happens at intake; bad exit rollers if happens at the output; broken connection of anti-static strip if paper sticks to drum.