My laptop's been super slow for like a week now, programs take forever to open and sometimes weird ads pop up even when I'm not browsing. I've got Windows 10 and the last scan with the antivirus that came with it didn't find anything, but I'm not sure I trust that.
Windows Defender (the built-in antivirus) is decent but sometimes it misses things, so it's not a bad idea to run an additional scan with another tool like Malwarebytes or HitmanPro - they're free and pretty reliable. Have you already checked if there are any weird processes in Task Manager (Ctrl+Shift+Esc)? It's also worth checking your browser extensions and programs that launch on startup, because that's often where annoying ads and junk sneak in. If it's still slow after scanning with Malwarebytes, it could just be that your computer is bogged down or your hard drive is almost full, which definitely slows everything down a lot.
Was it exactly a week ago or longer? Because if the weird ads started suddenly, there's a pretty good chance something's up. Besides the Malwarebytes scan that's mentioned above, you should also check what strange extensions or programs you have installed - go to Control Panel > Programs and uninstall anything you don't recognize or don't remember putting there yourself. One thing a lot of people miss: open Task Manager (Ctrl + Shift + Esc) and look at the Processes tab to see which ones are using a lot of CPU or RAM for no obvious reason - sometimes malware disguises itself with names that look legitimate but it's doing weird stuff in the background.
First thing is to check the task manager (Ctrl+Shift+Esc) and see what processes are eating up CPU or RAM in weird ways, especially if you see names you don't recognize or they're running from sketchy folders. If you spot something odd there, write it down and search for it on Google before you close anything. Then, like people probably already told you, run a scan with Malwarebytes or something similar in safe mode (F8 when booting), because it often catches stuff that your built-in antivirus misses since malware hides while the system's running normally.
Also check if you've got weird extensions in your browser or if the homepage changed on its own, that's typical adware stuff. If it's still just as slow after all that, the problem might not be a virus at all but a maxed-out hard drive, a stuck Windows update, or just that your computer needs to clean up temp files and defragmentation, but start with what I'm telling you since it doesn't take long.
Ads you're seeing without even browsing are a pretty clear red flag, so yeah it's worth digging deeper than what Defender found. Besides running Malwarebytes like they mentioned, check Task Manager (Ctrl+Shift+Esc) and sort by CPU or RAM usage to see if there are any weird processes eating up resources - if you spot something with a suspicious name or running from strange folders, write it down and Google it before you touch it. It might also be worth checking your browser extensions and installed programs in Control Panel, because sometimes those ads come from there.
Check if you have any weird extensions or toolbars installed in your browser, because ads that pop up when you're not even browsing usually come from there. Once you clean that up, you'll already know if the problem is actually malware or just junk that snuck in during a careless installation, so running an analysis with additional tools will give you a clearer answer.
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