Computer problem

OK, so, I was trying to open iTunes earlier because I wanted to be a song, but, when I click on it (from the start menu) it says:

"Windows cannot open the specified path, device, or file. You may not have the appropriate permissions to access this item"

It also happens when I click on other things, like calculator, notepad, etc.

My computer is a Windows Vista COMPAQ, just so you know.

P.S. My computer was recently infected with viruses and my mom's friend had to fix it. Could it be this? The first few days after he fixed it a window kept popping up saying some default programs had been disabled for my computer's safety. I hate those things, though, so I ignored it. I also went to control panel and set every basic program (Media Player, Internet, etc.) to have all it's defaults, but it didn't work