Up until 2 weeks ago I was able to print PDF files

Hi,
u did not mention which operating system, if u r using xp then click on start go to controlpanel , and controlpanel click on printer and faxes and if u r using
vista or windos 7 click on start go to controlpanel , and controlpanel click on printer,
1.under printer icon u can there would b a tab "add a printer"
2.u will get a new window select "add a local printer" click on next
3.select the port usb virtual 001 for usb connection and select lpt 1 for wireless, click on next
4.on the next page on the left hand side select HP and on the right hand side select deskjet 990c printer
5.and know that u r not using this printer
6.click next use this printer as a default one
7.it will give u an option to print a test page
8.click on "no" and hit next
9.now try to print and check

You can try to restore your computer to a time/date when things worked correctly: Start-Programs-Accessories-System Tools-System Restore. This process is fairly quick.