I have a PIXMA MP830,

Hi there,

This sounds very much like a problem with a clogged print head. Have you tried both the standard and deep-clean options via the printer driver? These problems occur quite regularly with inkjet printers, especially if an ink cartridge has been allowed to run dry and has been left to stand for a while. head cleaning fluids are also available from many shops online, but in a worst case scenareo, a replacement head may be required.