I have Windows 7 Professional 64bit SP1 and for the last few weeks occasionally I've had the issue that I can no longer click on / use anything other than the currently open application. And even the currently open application window controls (close, minimize, maximize) can't be clicked. Similarly the taskbar icons and start menu can't be activated via the mouse. I can bring up the task manager with CTRL + SHIFT + ESC but once open the same issue is evident with it as well - I can view tasks/processes (at least those listed in the first scroll page) but I can't click on anything. Task manager isn't reporting any unusual memory or CPU usage at such times. The only ways to stop this that I've found are either to wait (leave the PC alone for ages) or do a hard reboot. I can't think of anything that I could have installed in the last few weeks that might account for this behavior. It also doesn't seem to be linked to the application I'm currently using (i.e. sometimes I could be using Firefox, other times Chrome, IE, Photoshop, Word or something else). My system is set to download and apply all updates automatically. Am using Microsoft Security Essentials and it's reporting everything OK. Dell XPS 17 notebook, 8Gb RAM, 2 x 256Gb SSD

See if the issue occurs in Clean Boot. If it doesn't, re-enable things in groups to narrow down the culprit. You might also want to download and run MalwareBytes in Safe Mode to check for malware. Jerry