YES!!! Finnaly, after almost a week of really painfull research, I have found the culprit: a local installed network printer driver.
Today, I have found a consistent way reproducing the problem. After noticing that it ceased whenever I stopped Printer Spooler service. After some trial and error, a thought came to my mind:
"What if the problem only arises when someone else create a printer job?"
"May be sending a printer test page and, imediately, double-clicking my EmptySample.xls may cause the hanging behaviour?"
Lucky (?) me, on first attempt, Windows Explorer imediatly froze! Full of joy, I have replicated the experience a couple more times and Yes!. Almost one week later, I was able to consistently reproduce the freezing/hanging/lack of responsivenesss or what we may call it!
I have also noted that some installed printers were using a direct port and some where server shared printers. Reproducing the experience on server shared printers was okay. So, as far as I know, this issue only afects local installed network printer drivers.
That explains why:
- It was intermittent. Because it only happened whenever someonelse sender a document to printer;
- It only happended during regular work hours. After 6 p.m. almost everybody has leaved the building. So, there no one to triger print jobs;
- It dit not occurs whenever network cable was disconnected;
- Windows Explorer resumed regular document load imediately whenever I stopped Printer Spooler Service.
Even though, from now on, I will consider this a closed case, I will update this answer whenever there are new findings, specially, present you guys some Process Monitor's collected data that, in the paste few days, where pointing to Printer Spooler Services - I just was not prepared to understand the provided clues. I will work on that.
For whom whoever followed comments or revisions to this question, please, forgive me for doing so many updates, but I really think that keeping you updated was important.
Thanks a lot to everyone!!!