Do you have a digital TV with an HDMI connector and your computer only has a DVI one? Or the other way round, your monitor has a DVI connector and your computer uses an HDMI one? Then you need an HDMI to DVI Cable (Or a DVI to HDMI cable, they’re the same thing).

These HDMI to DVI cables will still support up to 1080p (Full HD) resolutions; However as DVI does not support sound you will have to buy a separate audio cable. 

A DVI to HDMI cable can also be used in place of a DVI to HDMI adaptor or DVI to HDMI converter.