Getting hacked?

Recently I noticed someone on my email address trying to change my maplestory info.. I don't even play the game anymore but i'm concerned that someone got into my email address. I'm assuming there's a keylogger on my PC, is there a way to find it and remove it somehow? I have avast antivirus but it's mostly useless and doesn't detect anything even when i'm suspicious I have malware

EDIT: I typed this up in a hurry but i'm looking for a step by step guide on how to clean out my PC.. so I can change all my passwords around freely without worry