The only sure way is to do a clean reinstall of the OS from the original Microsoft DVD (assuming it's Windows 7) yourself. Then add the other "some basic software" the same way, from the original source. And there's your clean system.
The person who installed some basic software on my pc turned out to be really shady and untrustworthy. I don't trust him at all and think he has "bugged" my pc to monitor what I do. This isn't paranoia, I have good reason to suspect him. How can I find out, without asking him, of course?