Hpdeskjet940c won't print

reistallation of printer

1 Do self test without connecting to computer, if page prints properly print engine is ok.
Note this does not test function of input port at back of printer.
2 Test usb port from computer by connecting to another known working device. (Another printer, or Scanner).
3 No response change USB cable for anorther, if cable tests ok connect to 940c printer. if still prints garbage, input PCB is shot. Buy new printer.
Ps. The fact that your printer is printing garbage means it is getting instructins from your computer, A fualty computer USB port. the connencting cable, and the USB input can corrupt a good signal from the compurter.