black screen on lenovo s10 ideapad?

It sounds like it is going to sleep.

Press the Fn key to wake it up.

If it has gone into hibernation then you need to press the power button.

I use to have that exact problem with a laptop. What I did that seemed to help was change the power settings. Turn off "after x minutes/hours" enter standby/sleep mode. I don't know specifically, but I assume, that some laptop chipsets and OS are sometimes a bit buggy in this area. Let your laptop/chipset/motherboard maker brand know of this.

Or...Maybe you should update the bios and/or reinstall the operating system.

To wake from sleep mode: press spacer bar once.

To wake from hibernate mode: press power button once.

If it still does not load operating system then most likely the OS has crashed due to corrupt operating system files or virus/malware/spyware. Repair or install new OS using a set of recovery disc.

If in warranty take in for repair.

I have never used the computer that you have. But normally you can set the battery settings. If you right click on the battery icon it should give you options. If it says power options click on that and let the page open. You should be able to change your power plan or the settings now. And when it says sleep or hibernate set the timing to never and that should solve your problem.