The laptop has a 15 pin VGA connector
The TV has a 15 pin PC type VGA input.
A standard 15 pin VGA lead chsould interconnect the 2 - use one with all 15 pins included/connected.
Also ensure you have the correct and latest graphics card drivers installed on the laptop.
Find out (laptop manual which is also downloadable as a PDF file from Dell support) what key combination switches laptop VGA port between laptop screen, screen+ external video out and video out only (not on laptop screen). Function key + f8 on this laptop, Fn + F5 on an older Dell laptop.
If you want audio through the TV you can interconnect the laptop headphone or audio output with the TV audio input too.
See numerous previous questions about connecting laptops to TVs (use "search this forum" tool with suitable search term or terms).