It's a software issue because when I take a screenshot there's nothing wrong
Pelo contrário, isso significa que é um problema de hardware. As capturas de tela não são feitas pela leitura do LCD físico, elas são feitas pela leitura da memória interna.
Você provavelmente precisará reposicionar os conectores ou substituir a tela.
Veja o que a Dell diz
The most common cause of these lines is simply a loose connection. As notebook systems are carried around, no matter how careful we try to be, they have a tendency to be bumped, jarred, and even sometimes the heart stopping drop. Though today's notebooks are designed to better absorb and dissipate small shocks, it can still have adverse affects on the notebook's internal components. A good bump or series of bumps and random movements can cause the LCD cable to become loose.
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If these simple fixes don't seem to work, then we need to look at the actual failure possibilities. Vertical or horizontal lines that don't disappear after the basic troubleshooting are usually caused by circumstantial failures. The most common type of failure that leads to lines on the display is an open circuit connection between the driver IC (flexible circuit board) and LCD glass. This is usually caused by external stresses (mechanical, thermal, etc…), which causes the flex circuit to detach from the glass.