So my computer was running very very slowly (so much that you can't go to start menu or open anything). Starting up is also very slowly, takes up to 8-15 minutes. And then after logging in it takes another five minutes. I recently upgraded to Windows 10 and but I didn't really like it so I upgraded it back to Windows 8.1 and it became very slow. The cursor works fine (not a slow cursor). CTRL+ALT+DELETE takes up to 20 seconds to load. To click a something (desktop icon, start, etc etc), it takes a very long time like 10 to 20 minutes. My PC is a 64 BIT, Lenovo, Windows 8.1, and its about one and a half years old. Before I upgraded to Windows 10 it was working fine but after I changed back to Windows 8.1 it suddenly was very very slow.
Please reply soon, thanks.