If you can identify a point where the problem started - for example when you installed some software - then uninstall the software. If during your `uncluttering` you changed settings it is going to be difficult to help unless we know what you changed.
I could be that you have installed a lot of security software which is conflicting. To try and find out if this is so, open Windows Task Manager and check the CPU usage to see which software packages are using most. You should see little activity normally with System Idle Process generally above 95%.