Rodolfo's laptop "started to slow down 2 days ago." A number of factors can cause that change.
Let's start with the easiest and most obvious fix: Have you rebooted lately? A lot of people leave their PCs on 24/7, or put them into sleep or hibernation mode rather than shutting them down completely. But a simple, full reboot can clean out a lot of Windows' temporary cobwebs.
Did that do the trick? If not, we'll have to do some detective work.
[Have a tech question? Ask PCWorld Contributing Editor Lincoln Spector. Send your query to firstname.lastname@example.org.]
Ask yourself what's changed recently. Did you install a new program? New hardware? Updated a driver? If so, try undoing what you did.
You can uninstall a program from Control Panel's Programs and Features tool.
Suspect a driver? Search for and open Device Manager. Then find and double-click the new driver. In the resulting dialog box, click the Driver tab, then the Roll Back Driver button. If that button is grayed out, the problem isn't with that driver.
If you added new hardware, remove it, then go to Device Manager, find the device, right-click it, and select Uninstall.
Find the bad process
None of those panned out? Then look for an overly large process that's hogging the CPU or memory. Right-click the taskbar and select Task Manager or Start Task Manager. Click the Processes tab, then the CPU column header.
If there's one big hog clogging the CPU, you'll see it. And you should be able to tell by the name or the description which program launched that process.
You can also click the Memory column and see if there's a hog there, as well.
Closing that program should fix the problem temporarily. If not, go back to Task Manager and see if the process is still running. If it is, select it and click End Process.
That's only a temporary fix. To kill the problem permanently, find a better program that does the same job, then uninstall the application that was causing the problem (and let the publisher know why you stopped using their program).
Scan for malware
Malware rarely causes a serious performance hit. The last thing cybercrooks want is for you to get suspicious. But it's worth looking into. Follow my previous advice for discovering and tracking down malicious code.