If you did not install a monero miner, your machine is probably compromised. You'd need to first update your OS and other programs to close the breach which allowed the attacker to compromise your machine, then remove it. The first step is important or cleaning it up will not prevent it from being compromised again. I can't help you about the details, but there are various free antimalware programs for Windows which might help (though careful to lookup names first to check which are legit, as some malware apparently purports to be antimalware in a bid to get run).