Coombs' test involves taking a blood sample which is checked for the presence of antibodies which may destroy red blood cells.
You can use the HP Print and Scan Doctor to test the status of the printer spooler, print queue, device manager, and device conflicts. 1  On the desktop, double-click the HP Print and Scan Doctor icon to open the tool. 2  Click Start on the Welcome screen. 3  Select your printer, and then click Next.  Click Fix Printing.
Restart the computer. When the computer has finished restarting, click the Apple icon (), and then click System Preferences. Click Printers and Scanners, Print & Fax, or Print & Scan to open the Printers list. Click your HP printer in the Printers list, and then click Open Print Queue.