Hi Nina,
1. Have you made any recent changes on your computer prior to the issue?
2. Are you able to print from any other application?
Perform the following troubleshooting methods:
Method: 1
I would suggest you to run the printer troubleshooter and check for the exact issue.
View the following link to run the printer troubleshooter.
Open the Printer troubleshooter
Method: 2
If that doesn’t work I would suggest you to uninstall and reinstall the printer driver and check how it works.
Follow the steps to uninstall and reinstall the printer driver.
a. Go to Start and select Control Panel (Classic View)
b. Select System icon, and click Device Manager on the left.
c. Right-click on Printer drivers and select Uninstall.
d. Restart the computer.
Follow the steps form the following link to install the drivers for the printer.
Using the Add Hardware Wizard to Install a Driver Package
You can download the printer driver form the following link.
http://www.support.xerox.com/support/phaser-6300-6350/downloads/enus.html?operatingSystem=win7