A lot of spyware and adware along with a few viruses can make a real mess of your PC. One of the problems you're going to see is that some of the files that load up will resist deletion by AV/Adware programs. Once you identify the files and the locations, boot from a floppy/CD or run safe mode from the command prompt, then delete the files manually. After you start again, you will get error messages from the registry keys leading to missing files. Delete these reg keys. This method is fairly effective, but requires a little know how.

<span style="color: lightblue">And so Ad-Aware and Spybot both offer to run at the next system startup, before processes are loaded, if they try to delete a file that is locked from them.