Completely and correctly scanning your computer for malware like viruses, Trojan horses, rootkits, spyware, adware, worms, etc. is often a very important troubleshooting step. A simple virus scan will no longer do.
Many forms of malware cause or masquerade as seemingly unrelated PC issues like Blue Screens of Death, issues with DLL files, and other serious Windows problems so it's important to properly check your computer for malware when working to solve many problems.
Note: These are general steps to scan and remove malware from your PC and should apply to any Windows operating system.
Download and run the Microsoft Windows Malicious Software Removal Tool. This free, Microsoft provided malware removal tool won't find everything, but it will check for "specific, prevalent malicious software" which is a good start.
Here's a list of everything it will find and remove.
Note: You may already have the Malicious Software Removal Tool installed. If so, make sure you update it using Windows Update so it can scan for the latest malware.
Update your anti-virus and any anti-malware software installed on your computer.
Before running a virus scan or malware scan, you need to make sure the virus definitions are up to date. These regular updates tell your anti-virus software how to find and remove the latest viruses from your PC.
Important: Don't have a virus scan program installed? Download one now! There are several free anti-virus programs available so there's no excuse for not running one.
Run a complete virus scan on your entire computer. If you have a dedicated malware scanner that does more than look for viruses, run a full scan using that program too.
Note: Don't simply run the default system scan which may not include many important parts of your PC. Check that you're scanning every part of every single hard drive and other connected storage device on your computer.
Important: Make sure any virus scan includes the master boot record, boot sector, and any applications currently running in memory. These are particularly sensitive areas of your computer that can harbor the most dangerous malware.