If you suspect that the print head could be partly blocked, you can check this out by getting the printer to perform a test pattern.
Most printers can do this, either from the printer driver software (in Windows XP, click on Start, Printers and Faxes, (right-click on the relevant icon), Properties, Maintenance, Test Pattern), or by some button-pressing on the printer itself, or both.
Look at the output to see what’s missing.
Ink or toner empty:
Be aware that readouts showing an ink tank to be part full may not be telling you the truth.
In many cases, to the great surprise of owners, these are not a measurement at all, but the output of some clever software making a guesstimate of how much ink is remaining based on the amount of printing and purging done.