hi, talking about an hp probook 650g1 the screen have 1/4 of the surface that doesnt work, it could be alternatively white / with stripes / or working, it change if i hit him (slowly ) in the lower right part of it...how to understande if i need to replace the screen or the cable?? thanks
link to the image
To be honest, it could still be either the cable or the display.
The only way to know is to open up the laptop and check the cable to make sure it isn't loose or damaged. Then if that doesn't resolve it, replace the cable. If still problematic, then replace the display.
Unless, of course, it is under warranty. Then contact the manufacturer about a repair. If it isn't under warranty, and you don't want to have to purchase the parts and/or do the work yourself, then try a local tech.