[Help] PC problem.

My cousin is currently experiencing a problem with his PC.
He starts the PC, Windows XP is loading fine.
His problem is, cannot open .exe files. He is able to copy/paste, create new folders but when it comes to .exe, nothing happens Task Manager ( Ctrl + Alt + Delete ) also isn't showing up.
Any tips if that is virus causing it or it's just the OS?
If so, how should he fix it?

He should do a full system scan with Malwarebytes: http://www.malwarebytes.org/

If it is a virus: download Malwarebytes for free. run it and let it update. then scan his pc.

If that doesn't work: reinstall windows

Thank you both, I completely forgot about that program..