Computer randomly stops opening executable files. (.exe)

My Windows XP computer acts fine for a while, but usually after it sits running unattended for a while, I will come back and try to open the web browser and it does nothing. I crtl alt del it and task manager will not even open. Then I try several other programs such as firefox, chrome, MS Word etc. and they will not open, it just basically ignores my request. The only thing it will open is folders such as my documents or my pictures... I am totally stumped and I just can't figure it out I've tried searching google for it but nothing really helps. Is the harddrive going bad or could it possibly be corrupted files or a virus? thanks what would cause it to wait a while to stop working??, it works fine then it just stops responding?

You've got nothing to lose by trying the malware removal area.