Need help with computer timing out.

[Blighty]

The button in the bottom left corner used to be called Start. Doesn't seem to have a name anymore.

Start > Settings > System > Power & sleep
Brings up a screen like attached. Adjust here.

In addition, the computer manufacturer may have their own settings. For example, a Dell computer may have their own Power & Sleep settings. Check if there is any form of settings / set up for your computer.