Printer inks dry up easily in warm weather. Run the head cleaning utility. There are various ways of accessing it (depending upon the make & model of printer) but this should work for all printers:
Go to your Printers folder. (In XP that's Start > Settings > Printers & Faxes. It's similar with other versions of Windows).
RIGHT-click on the icon for your printer. Select 'Properties'
Click on the 'Maintenance' tab and then on 'Head cleaning' (or something similar).
After it's finished run a 'Nozzle Check'
You might need to go through the procedure several times before the problem clears.