open up your case and check for dust. - if dustly take into a well ventilated area and spray with one of the CO2 canisters.
do a boot time scan (virus scan, malwarebytes and spybot S&D)
download and run CCleaner, tick "old prefetch data" and "environment path" as well as everything from the Applications tab - delete whatever it pulls up
do a full system defrag. - using either defraggler or auslogics disk defrag.
check for driver updates for anything that you have installed.
If problems started after installing something or a system update, roll back to an older configuration and see if that helps.
If none of these things work its time to start looking at hardware faults...
A good list, I'll start going through it.