I found that same issue on mine as well and went round and round until one day I found that what was happening is that there is a corrupted screensaver I was using that was trying to activate while system was idle. Once I uninstalled the screen saver or set the option to (NONE) the problem disappeared. Simply I later found that the screen saver that was installed had a little known capability of accessing the internet in the background looking for updates and would lock up because the Firewall and AV I use would go nuts trying to stop it's repetitive attempts to do so. Screensavers that are freeware are set to log onto and coneect via the net automatically as a means to let the creators know who is using their software and when. Not quite a keylooger type method, but more like a web site counter would do but incorporated within the program itself. They are boarderline trojan horses completely legal unabtrusive attempts the developers of the screensavers do to see who is popularizing their products. Where they cross the line is when they lace that capability with the collection of MRU data from off of your computer in the background and sell that information to spammers, advertizers and hackers. So unless yuo know for sure and or pay for a screensaver download from somewhere safe I recommend getting rid of any free ware, period. Sometimes System builders include freeware with their software bundles in order to sell their products. I tell people buying brand new off the shelf units to back up their Program files and drivers they want to keep then reformat their HDD immediately for this very same reason, even before physically connecting to, or accessing the internet.
So like I said turn off your screensaver and see if the problem still exists, if not then see what screensaver is being used and has been downloaded so you can remove it. If there was a corruption in the Windows screensaver files then go into Windows Components /Accessories files and disable the WallPaper, and Themes.
