Click "Start" (big button, bottom left of the task bar)
Find "Accessories" > "System Tools" > "System Restore"
It will ask you what date you want to go back to...select and let it do it.
It wonÂ´t take long but youÂ´ll need to restart your computer afterwards.
Also, download, install and run "Malwarebytes" to check for anything nasty that might have gotten in, and have a look at your task manager - whatÂ´s running there...youÂ´ll probably find 40 or 50 processes, but itÂ´s possible some of them are causing problems (maybe we should look at that later)