A black screen is really two problems wearing the same face. Either the laptop is not running at all, or it is running fine and only the display is dark. Those need opposite fixes, so before anything else you have to find out which one you have. One test settles it.
Is it actually on?
Put your ear near the machine and look for signs of life. Fans spinning, a hard drive ticking, keyboard lights, a glowing power button. If it is silent and dark with no lights, this is a power problem rather than a screen problem, and you should switch over to computer won’t turn on, which walks the no-power checks in order.
If you can hear fans and see lights but the screen stays black, good. The computer is alive and the fault is in the display path, which is a much friendlier place to be.
The external monitor test
This single test tells you whether to blame the screen or the computer. Plug the laptop into an external monitor or a TV with an HDMI cable, power the second display on, and press the key that switches display output. On most laptops that is the Windows key held with P, or a function key with a little monitor icon on it.
- Picture appears on the external screen: the computer and graphics are fine, and your laptop’s own screen or its backlight has failed. That is a repairable display, not a dead machine.
- External screen stays black too: the problem is deeper, in the graphics hardware or the boot itself, not the panel.
Knowing which side of that line you are on saves you from replacing the wrong part, which is the most expensive mistake in this whole game.
When the backlight is the only thing dead
Tilt the screen under a bright lamp and look very closely. If you can just make out a faint desktop, the ghost of icons in the dark, the display is working but its backlight has gone out. The image is being drawn, there is simply no lamp behind it. That is a specific and often affordable repair, and it is worth naming precisely when you take it to a shop so nobody replaces the whole panel.
Before you conclude any of that, rule out the silly stuff: the brightness turned all the way down by a stray key combination, or an external monitor setting left active so the laptop is dutifully sending its picture to a screen that is not there. Both produce a “black screen” on a perfectly healthy machine.
The reseat that revives a black boot
If the external monitor stayed black too and the machine seems to power up but shows nothing anywhere, one hardware fix is worth trying before the shop: reseating the RAM. A memory stick that has crept loose in its slot stops the computer from booting far enough to send a picture, and it produces exactly this dead-but-humming behavior.
Power down fully, unplug, open the small access panel on the underside, and press each memory stick firmly back into place until the clips catch. On plenty of “black screen, fans running” laptops that one reseat brings the picture straight back. If it does not, and the external test also failed, you are into graphics-hardware territory where a shop takes over. For everything downstream of getting the picture back, the tune-up in how to fix a slow computer keeps the machine healthy once it is running again.