Microsoft has pushed out an update for the Windows 10 technical preview that it released on Tuesday which will fix the power or sleep issues that your install may be exhibiting.
The update is out now and you can grab the bits by going to Windows Update within the PC settings and checking for updates.
This is a relatively quick patch for Microsoft seeing as the build was released this week, which makes us think that this was likely a known issue before the release. Regardless, the patch is out now and if your machine has had any issues with power / sleep functionality, this should fix it.
We have been covering all of the new features that shipped with the latest build of Windows 10, 9860. Everything from new animations to Battery Saver and Data Sense have shown up in this build. If you happen to find something that we have not covered yet, make sure to send us a tip. Or, if you are having issues with your install, you can get help in our forums here.
Source: Microsoft