This worked for me on Windows 8 (along with every other Microsoft OS I have used). I went from 100% CPU usage and 100% Disk usage to this! (See first pic)
This tek can also be found in my journal with other cool stuff
Lets begin
*Open-up the task manager. Press "Crtl + alt + delete" then select task manager from the list to open or just right-click the bottom left corner of the screen and click "task manager" from the list.
*Now evaluate how the computer is doing by looking at the CPU, Memory, and Disk usages under the "performance" tab. We want these percentages to be as low as possible to have the resources to run the computer smoothly.

*Now click over to the "Start-up" tab. I then cross-reference the startup names online at
http://www.bleepingcomputer.com/startups/ to see if I need the app or not. Remember, every start-up app that is enabled is taking away from the computers resources to run. So the goal for top performance for the computer is to rid the start-up's that we are okay with being gone. (Notice how I do not have that many start-up apps. This is because I just restored this PC to try and fix a hardware/driver issue. You will have many more start-up apps then in my pic and brand new computers are always loaded with junk that needs rid of.


*Okay. Now restart the computer after disabling all the "startup" apps you are okay with loosing (most apps are not needed and are put on the "startup" list with the install of a new application).
*Now comes the fun part. Sometimes, software will run in the background (that is not listed in the start-up tab even though they startup with a restart) and go crazy by stealing all of the computers resources. For example, their was a manufacture, factory application on this computer that was causing CPU spikes every other other second from a normal CPU range of 10% - 30% (while idle, for my pc) to a CPU range of 90% - 100%. This is a common problem for many computers.
Applications just go fucking crazy sometimes like people do and need delt with.
Now, to hunt down these applications that have crazy. In the "Task Manager", click on the "Process" tab. Here is a picture. Note, my percentages are very high because windows is updating in the background. Not sure if windows updates does this to
most computers (I find this common among most of the computers I have been on).

In the process tab, we are looking at the applications that are using all the resources. So that we can correct the issue. For example, if high CPU is a issue then we would be looking at the app or apps that are using all the CPU and either re-installing the software or just deleting the software. Note, the process screen may move quickly as the task manager is reading the usage in real time. For example, my crazy manufacture, factory application was causing high CPU every other second. So the application would show at the top of the list for a second then drop back down the list.
*After completing changes to the computer, restart the computer. Then check the computers resource percentages (while idle aka nothing is running that isn't started by a restart) look to see if their is an improvement. Sometimes, I will disable a process from the start-up list (or other location) to later find out that after a restart that the process is being enabled back on. Have to verify changes to computers (they do what they want, I still have flash backs of the "Blue Screen of Death".
Warning, these solutions may not be the problem to poor computer performance but I have found these to be the major reasons to cause a slow computer.
Other factors that can cause poor computer performance include:
*Damaged or old hardware
*Viruses
*Microsoft services that should be disabled if not being used
*Power settings
*Visual effect settings
*need to uninstall apps (usually, not an issue unless the application has gone crazy as described above)
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Still can't fix your PC?
Don't worry
I hate computers too!