I have a problem when shutting down or restarting my PC. A prompt window will launch asking to end task for QTSTimer. When the increasing bar finished, it failed to close and I have to manually click "End now" to continue shutting down the PC. Anybody knows how to remove or disbale the QTSTimer?

I have never seen this problem before. A search reveals little, but shows it has been around for at least 4 years. One site reports it may be spyware.

So, security first - I recommend purging the system of clutter and running through a complete malware scan - see Cleaning Out Malware if you do not already have a complete arsenal of tools. Once done, if the problem still occurs, uninstall anything related to QuickTime.