A process called Service Host: Local System is using up all of my laptops resources

I had this same problem.  Open up resource monitor.  Some processes are not displayed on task manager and are only viable in Resource monitor.   It is likely that one or more process is in an infinite loop.  You can easily identify these because they take up a full logical core on your processor.  I have a quad core so I look for processes taking up exactly 25% (it would be 50% for dual core).  Right click on it and select suspend process (make sure all your application are closed and all data saved in case removing the process causes instability).  Your CPU should drop down to a low % utilization, your laptop will be much quieter. cooler, it will consume less power, and will run faster.

If you ever feel like the fan is extra loud for what your running I would go through this check.  The most likely cause for these corrupt processes is because you downloaded and installed free-ware.  Although free they come with lots of piggy-back downloads and change a lot of settings on your computer.

Just expand that process('Service Host' which is killing most of your RAM) in Task Manager and end task of some useless programs ; on my case I had to kill "THEME" and it worked. Remember if you kill the whole service host process it will disable NETWORK on your pc.

just go to control panel and select services navigate to something like background intelligent transfer just  "STOP" the service  you are done. if u again see the same issue try repeating the same because it will automatically restart after boot.

hope this may help a lot..

Unfortunately, none of these suggestions help. Some of these sub-services can be stopped and others usually can't.  In some situations, though, I can stop the entire service, but then it crashes my PC. The problem remains upon reboot.

I spent a few hours on the phone with Microsoft support in order to solve this problem, and they, too, were baffled by it.

The good news is that I finally got it solved. BUT, upon their suggestion I had to do a fresh install of Windows 10. I was apprehensive about it, but the rep assured me that I could do it without harming any of my personal files. So, while on the phone, I went ahead and did the clean install (I had previously upgraded from Windows 8.1 to Windows 10 months ago). The system clean install process assured me that none of my files would be altered. That's an issue up for debate!

Upon the fresh install, the problem with that processes constantly using high CPU went away and never came back! HOWEVER... while my personal files were preserved,  all of my Windows Live email was wiped out! So were all of my installed applications. The application restore was a pain, but within a few hours I had most of them reinstalled. But I really hated to lose my saved email. I wish I would have been warned about that, since I considered that data part of "my personal files".

In conclusion, because the high CPU process problem went away, and most of my old software was reinstalled without the problem returning, I'm concluding that the problem was not due to my hardware or installed software, but rather to a problem with Microsoft's update from Windows 8.1 to Windows 10. Others in the past have recommended a "clean install" of a new operating system. I now strongly support that recommendation.

My CPU was running at 35% and the Service Host: Local System was running at 33%. There were 20 items listed under the Local System. The only way I was able to solve it was by running Norton Power Eraser. The number of items listed reduced to 17.  Service Host: Local System now stays at 0% CPU usage and total CPU stays around 3%.  I do not know what 3 items were removed. But this solved the problem.