There's a problem with my laptop.Does it sound like a hardware problem or a software problem? details...?

One night, I left my computer on all night in standby mode, and when I turned it on there was a thin, flickering line at the top of the screen. The line alternated between the right side and the left side, and then disappeared completely after I turned the computer off and then back on. It has never happened since then, and it was a one time problem. Does this sound like a software problem or a hardware problem?

You have kept the your laptop in stand by mode for about 10 hour, It means that the Dispaly of your laptop may not stand on for long hours. After your turned of  the display Line was gone. It means that may be some jurk in the signals.

If you have any doubt regarding display make sure you  visit the Service center, expain the problem, they will explain the what's the issue is? 

Don't always keep the laptop in standby mode, Enable Hibernation. Keep your laptop in Hibernation mode, That's better for your laptop.

It's not the problem of software, It's completely related to Hardware. It depends upon the which company's laptop you are using and how old the laptop is?

I too faced the same problem with my laptop, I just opened my laptop and just cleaned with my blower. Display was corrected automatically. I don't know exactly what I did with the laptop.