Let me first say that I do not think that the issue I'm about to describe is the result of any virus, malware, etc. I've got my computer about as protected as it can be, and Panda Cloud Antivirus, Spybot S&D, & Malwarebytes have been regularly updated, run, and have been returning "clean" results for several years.
My laptop, an ASUS K50ij, is far from new. It runs Win 7 Home Premium 64-bit SP1, has a Pentium T4500 dual-core @ 2.3GHz, and the maximum 4GB of RAM.
When this issue occurs I've looked at Windows Task Manager the CPU is nowhere near to maxed-out and I've generally got at least somewhere around 500 Mb, usually closer to 1Gb, RAM still available.
The behavior is not immediate, nor even generally shortly after booting up. It can take anywhere from several hours to a couple of days before it rears its ugly head again, but it always occurs. Out of the blue the system slows to a crawl, the disc activity light goes on solid (no perceptible blinking at all), and many of the programs running will go in to "(not responding)" mode for a period of time or just stay stuck in this mode. I can sometimes, not always, get the problem to stop by slowly exiting out of programs when I can, but that doesn't always work nor does there seem to be a single program (e.g., Chrome, Firefox, Thunderbird, Search Everything, or others) that is either causing this issue or fixing it when I can exit it gracefully. Most often once it starts the machine becomes so unmanageable that I tend to shut it down, gracefully if possible, but with the power button if a graceful shutdown gets stuck for more than 10 minutes (the latter seldom happens, most times it will power down reasonably quickly). It did seem to happen much more rapidly when I was using Opera as a web browser, but I have stopped using Opera and it still happens.
The following are the programs that are commonly "always up" when I'm using my laptop, along with the extensions/add-ons for each. In web browsers it is my habit to have multiple tabs open within a single window as opposed to multiple windows for the same browser open at once.
Extensions: Adblock Plus 2.6.6
Classic Theme Restorer 22.214.171.124
Colorful Tabs 25.7
Appearance: Nuvola 1.32.1
Plug-Ins (Always Activate):
ActiveTouch General Plugin Container 29.1.2013.906
OpenH264 Video Codec provided by Cisco Systems, Inc. 1.1
Shockwave Flash 126.96.36.199
(Ask to Activate):
Adobe Acrobat 188.8.131.52
Google Earth Plugin 184.108.40.2061
Google Talk Plugin 220.127.116.11
Google Talk Plugin Video Renderer 18.104.22.168
Google Update 22.214.171.124
Java Deployment Toolkit 7.0.670.1 10.67.2.1
Java Platform SE 7 U67 10.67.2.1
Microsoft Office 2010 14.0.4761.1000
Microsoft Office 2020 14.0.4730.1010
PDF-XChange Viewer 2.5.311.0
Photo Gallery 16.4.3522.110
QuickTime Plug-in 7.7.4 126.96.36.199
Silverlight Plug-In 5.1.31211.0
VLC Web Plugin 188.8.131.52
Canon iMAGE GATEWAY Album Plugin Utility for IM 184.108.40.206
Add-Ons: Google Contacts 0.7.12
Provider for Google Calendar 1.0.3
Google Chrome 39.0.2171.95 m
Extensions: Adblock Plus 1.8.8
Cisco WebEx Extension 1.0.1
Google Cast 14.1113.0.4
SHOOT THE COOKIES by McVitie's 1.4.1
(all but Cisco WebEx are enabled in incognito)
I have tried every trick I know of in an attempt to figure out what it is that puts the machine into this state, but have done months of research and some tweaking (e.g. turning off indexing) and untweaking when a given possible proposed solution had no effect. Now I'm hoping that someone else in the cohort has experienced this same behavior and may be able to give me the guidance necessary to get this to stop happening.
Thank you in advance for any help you can offer.