There can be several different reasons why a computer monitor may not display the correct resolution. Poor connections, outdated drivers, settings that have been changed incorrectly, and damage to the monitor are all potential causes.
One of the most common reasons for a monitor not displaying the correct resolution is a loose connection between it and the computer. This can be due to improper installation, like when a cable is not correctly or fully inserted into a port. It can also become loose over time, especially if the cables are moved around frequently. To fix this, check all the connections between the monitor and the computer, making sure they are firmly in place. Also make sure that the right type of cables is being used (DVI or HDMI, usually).
Drivers can also be a factor in resolution display issues. Outdated drivers can cause the monitor to be unable to reach its highest resolution, or even unable to detect the monitor at all. To fix this, update the related driver software from the manufacturer’s website.
Sometimes a user’s settings can be an issue. The resolution displayed on a monitor is often set through the operating system’s display settings. If these settings have been changed, either manually or mistakenly by software, then the monitor may not be able to display its optimal resolution. To fix this, open the display settings and reset them to the recommended levels.
Finally, there is the possibility of damage to the physical monitor. A monitor that has been dropped, exposed to extreme temperatures or humidity, or been subjected to some other type of physical trauma may not work properly, including possibly not being able to reach the correct resolution. Any physical damage should be assessed by a professional to determine if the monitor is still usable.
If the problem still persists after checking all these points, it might be a good idea to take the monitor to a shop to have it looked at, as the issue may be more complicated than any of the above.