the problem here for troubleshooting, then, is that it worked a month ago. Something has changed.
I never download MS updates without researching and last month MS released an "application compatibility" update.
I looked into the update and several programs were to be "blocked" by the update.
I did not like the "to be blocked" list, so i avoided the download.
Perhaps something in this update has corrupted some aspect of CS5?
edit: i'm tired, thus i did not make myself clear: i know that you had typed that you did not install updates. I assume that you mean manually but i do not know if your system is set to receive automatic updates. I do not use automatic updates. I always research first, then manually install. I am just thinking that you may have automatic updates and one of the updates has changes something.
if you could look at your update history and report updates for the past month, then maybe we can see if there is a culprit in the list.
By the way, have you downloaded Windows 8.1 Update 1? you have until June to do so.
I figure that either an MS update has caused a problem, a driver needs updated, other Adobe products have updated something which is now causing a problem, or Win registry values are corrupt. You would remember tinkering with settings. If all else fails, then, I would try a system restoration point around March/April.
