|I agree that the first step is to install, update, and run Malwarebytes in Safe Mode with networking. remove all it finds.|
Run Disk Clean Up. Computer, right click on your hard drive>properties, choose Disk Cleanup, select all OK and OK to run it. It might take a while to show you the options and again to complete, depending on how much junk is bogging things down.
Remove programs from starting with Windows. Start, Run, type msconfig, go to Start tab, uncheck all except Microsoft labeled programs and your antivirus program, Apply and let it restart the machine. Anything you find that you really do want it to start with Windows, you can always repeat and add a check mark back again for that program.
If these steps do not get you flying again, post back results for more advice.
You have to be a little bit crazy to keep you from going insane.