When selecting sleep from the menu option, my computer does not stay asleep. It goes dark for a second and then turns back on.

collette134 wrote:

How can I reset my computer, so sleep mode is working?

If you touch any key it will wake up, yes...

Have you tried shutting down and restarting— then try your sleep and compare your results

if you have an issue try a SafeBoot How to use safe mode on your Mac - Apple Support to sort anomalies.