Canon SX printers like the IIg usually fail in two major areas, the fuser, and the AC power supply (along with the occasional pickup roller). Check the fuser first since its cheap and easy to replace: http://www.fixyourownprinter.com/reference/guides/fuser/sx

The printer could also have dirty sensors or loose wires. Check the paper out sensor switch and the toner cartridge contacts. Also re-seat the printer's formatter board.