Here’s a little tip for anyone like me still using Windows Vista who’s having trouble with the system logging/locking you out after a certain period of inactivity (usually 5 or 10 minutes). The two most common culprits for this are the screensaver settings or possible power saving options, both accessible from within the Control Panel. However, what isn’t obvious and what drove me mad trying to find, is that even if you have None selected as your screensaver of choice, it appears Windows still sees fit to still log the user out after the allotted period of time. This despite the fact that the On resume, require logon checkbox is greyed out.
After much headscratching and searching through forums, I eventually discovered that you can prevent Windows automatically presenting you with the login screen after a few minutes of inactivity by reenabling the screensaver, providing an extraordinarily large number and unchecking the On resume, require logon checkbox. No more interrupted video viewing!