Actually, the link provided by nikorr is for Windows 7 32-bit. You may need to uninstall the existing printer driver first before installing the new driver. Disconnect the printer from your computer. Then, on your computer, go to Start menu > Programs > Lexmark 3500-4500 Series folder > Tools > Uninstall. After the uninstall process, reboot your computer when prompted.
To reinstall the printer driver for Windows 7 64-bit, please visit the Lexmark website at http://bit.ly/b6TXD2. Simply follow the instructions on your computer screen to complete the installation.
Should you still need assistance, please contact us through email at firstname.lastname@example.org or chat with one of our customer advocates at http://bit.ly/boldchat (available Monday - Friday (US: 4:00am - 7:00pm EST; UK: 9:00am - 11:00pm GMT)).