If you're running an older Windows 10 Insider Preview build, you'll want to update your copy before Thursday, October 15, lest you want to turn your PC into a brick.
Microsoft warned users that in a few days, Insider Preview builds released between January 23 and July 9 will expire, and once that happens, Windows 10 won't boot. These builds are numbered 9826 and 10166. Build 10166 is the final Insider Preview release prior to the launch of Windows 10 RTM.
"When the build reaches the license expiration date, the system will automatically reboot every three hours," Microsoft forum moderator RajithR warned in a support thread with information updated on October 7. "Approximately 2 weeks after the license expires, the build will no longer boot at all."
If you let the deadline lapse, you can still recover your PC, but additional steps will be required.
Microsoft said that you'll need to create a bootable USB drive to upgrade your system to Windows 10 RTM and enter a one-time setup key. Unfortunately, this code won't give you a full license to Windows 10 or allow the operating system to activate.
After setup, you can continue to re-join the Windows Insider program to continue testing new features and releases ahead of commercial availability.
The most recent Windows Insider Preview build is number 10565, which brings features anticipated in the release of the Threshold 2 update next month. This includes an improved Edge browser, a smarter Cortana experience and a new messaging app that integrates with Skype.
Additionally, with Build 10565, Microsoft is looking at ways to make Windows 10 activation simpler. Moving forward, you can use your existing Windows 7, 8 or 8.1 key to activate Windows.
Build 10565 will expire on July 16, 2015. To check to see when your copy of Windows 10 will expire, you can type "winver.exe" into the Cortana or Windows search bar.
Keep up with Windows 10 news by reading our coverage