My desktop including the start bar keeps disappearing... Anyone know why?

I own a PC and no matter what I do my start bar and desktop keep disappearing. The only way I can run programs is going into task manager and run a new one that way. If I run desktop that way it comes back shortly, disappears, reappears, disappears and continues this until it eventually just doesn't come back. I would really like to know what's causing this. I have both Trend Micro Antivirus and Spy Sweeper running often and I quarantine everything it detects. My process list shows nothing out of the ordinary... No idea whats going on please help!