Security vulnerabilities or malware infections on Windows PC

Hey everyone, I'm pretty sure my Windows PC got hit with something nasty—I'm seeing random pop-ups, weird background processes eating up my CPU, and my browser keeps redirecting to sketchy sites no matter what I do. I've already run Windows Defender and Malwarebytes, but they're not finding anything, so I'm wondering if there's a deeper rootkit or a manual removal method that actually works for this kind of infection without having to nuke my whole system. Any help would be huge, thanks!